Abstract: Abstract: To improve the working quality of the brush-rolling cotton harvester and to meet the requirement of the ginnery of the seed cotton picked by stripping-type cotton harvester, the article optimized the working parameters of the brush roller and added the recycling structure matched with the brush roller, based on the problem in the trials of the 4MZ-3B brush-rolling cotton harvester. Also, the improvements included the structure of the cotton pushing roller, the cotton-boll separating and cotton conveying pipe, the airflow-cotton separating apparatus and the machine-mounted pretreating apparatus. Based on these the new 4MZ-3C brush-rolling cotton harvester was formed and the comparative trials were conducted in Anyang, Henan. Compared with 4MZ-3B brush-rolling cotton harvester, the 4MZ-3C type raised the picking rate and the recycling rate of cotton boll by 3.42% and 74.57%, respectively, and lowered the loss rate from falling of cotton, the rate of hanging cotton, the missing rate of cotton, the loss rate from cleaning impurities, and the impurity rate by 0.85%, 0.89%, 1.05%, 0.63% and 3.71%, respectively. The optimization of the working parameter, which was mainly the revolution speed of the brush roller, and the installation of the recycling structure directly optimized the picking rate and lowered the loss rate from falling of cotton, the rate of hanging cotton, and the missing rate of cotton, due to the enhancement of the picking ability and the efficient recycling mechanism. By reducing the contact area of the roller at the radial direction, the modified cotton pushing roller could avoid the blocking of the inlet of the air conveying pipe for cotton boll separation, which was caused by vine plants collected in the field twining with the roller, reducing the chance of the machine halt. The improvement of the cotton-boll separating and cotton conveying pipe from air-blowing type to air-suction type could form an appropriate negative pressure area at the inlet of the pipe to pull seed cotton and separate cotton-boll form it, and effectively increase the recycling rate of cotton boll and avoid cotton bolls to enter the machine-mounted pretreating apparatus, which would cause adverse influence on cleaning performance and the rank of seed cotton. The improvement of the airflow-cotton separating apparatus from mesh box type to tangent-guided type could perfectly separate air flow from seed cotton, and make sure that seed cotton could enter the cotton cleaner mounted on machine smoothly and with little airflow, and at the same time, solve the problem of transition between the air conveying pipe for cotton boll separation and the cotton cleaner mounted on machine. The machine-mounted pretreating apparatus was modified as one-cleaning and two-recycling type from one-cleaning and one-recycling type, the new type had 3 cleaning units, and a new configuration of them was made to make the best use of its cleaning ability to reduce the impurity rate and the loss rate of cleaning. China had a planting area of 3 796 690 hm2 in 2015, while the mechanized harvesting area was only 704 620 hm2, accounting for 18.56%, which urgently needs change. The new 4MZ-3C brush-rolling cotton harvester has the advantage such as low price, friendly maintainability and wide adaptability, and every index of it is better than the operation standard of cotton harvester, which can perfectly meet the requirement of cotton harvesting mechanization.