Abstract: Abstract: With the rapid development of intensive livestock and poultry industry, a large amount of livestock and poultry manure is produced every year in China, which will pollute the environment if not treated properly. Chinese government carries out the environmental impact assessment for these enterprises every year, and develops strict policy to restrain the waste discharge. Solid-liquid separation is an important procedure for the follow-up comprehensive utilization of livestock manure. The existing solid-liquid separation equipment has the disadvantage of low efficiency and poor effect when processing high-concentration fecal sewage mixture. This paper designed a new type of interrupted-whorl screw solid-liquid separator with the purpose of efficiently carrying out the solid-liquid separation of high-concentration sewage, improving the separation efficiency, and producing less additional sewage. As one of the key components of the separation device, interrupted-whorl screw was designed and it includes three components, i.e. feeding section, extrusion section and discharge section. To enhance feeding capacity, continuous screw was used for the feeding section. The extrusion and discharge sections adopt the interrupted-whorl screw. The screw pitch of feeding section is 140 mm, and those of the extrusion and discharge sections are 160 mm. With high-concentration pig manure (total solid concentration 21.18%) as experimental object, this study investigated the optimization of operating parameters on self-made screw extrusion separation test bed. The Box-Behnken design method was adopted in the operating parameter optimizing experiment of the Interrupted-whole screw dewatering device. The spindle speed of screw, gap distance, and counterweight position were taken as the influencing factors, and the separation efficiency and filter cake moisture content were selected as the responsive variables in the experimental study. The quadratic regression orthogonal experiment of 3 factors and 3 levels was designed; by using the regression analysis and response surface analysis with the software of Design-Expert 8.0.6, the mathematical model concerning the 3 factors' impact on the solid-liquid separation performance was set up, and the experimental verification of the mathematical model was also conducted. The results showed that the trial factors had great effects, and the separation efficiency and the extrusion moisture content could be fitted with two regression polynomials, the P values of which were less than 0.001, indicating that the models were highly significant. The coefficients of determination (R2) were 0.984 1 and 0.983 9 respectively, which showed that 98% of the response values could be explained by the models. According to the rate of factors contribution, conclusion can be given: spindle speed > counter weight position > gap distance. This indicates that spindle speed has the greatest effect on the separation efficiency among the three selected main factors followed by counterweight position, and gap distance has the minimum effect. This conclusion is consistent with the experiment results of GuanZhengjun which extracted water of cow dung by continuous screw separator. It shows that the spindle speed has the main impact on separation efficiency whatever used for interrupted-whole screw or continuous screw .Besides, according to the contribution of filter cake moisture content, it can be ranked gap distance > counter weight position > spindle speed. It shows that in the three main factors which are selected, the gap distance has the greatest effect on the filter cake moisture content followed by counter weight position, and spindle speed has the minimum effect. In conclusion, the interrupted-whole screw has great significance on reducing the filter cake moisture content. Through the experiments combined with the actual production, the final optimal combination of working parameters was concluded, namely the distance was 37mm, the speed was 56 r/min, and the counterweight position was at the 309 mm (relative location). The values of separation efficiency and extrusion moisture content were respectively 5.43 m3/h and 53.52%, and the removal rate of suspended solids removal rate was 54.91%. Both of the relative errors between the experimental and predicted values of separation efficiency and filter cake moisture content were less than 10%, indicating that the multivariate regression model was reliable. This research provides a reference to the parameter optimization of the interrupted-whorl screw dewatering device, and helps the development of the solid-liquid separation technology of high-concentration and high-viscosity pig manure.