Abstract: The purpose of this study was to investigate the effects of different proportions of aged paddy rice replacing corn on the physicochemical characteristics, pelleting characteristics and product quality of corn soybean meal mixed powder, and the processing parameters under different replacement ratio were optimized and the best replacement ratio and process parameters were obtained. In this experiment, aged paddy rice, corn and soybean meal were used as feed raw materials, ground by a hammer mill with a sieve diameter of 2 mm. mixed evenly in a mixer according to a certain proportion, three samples of mixed powder were randomly taken and stored in a sealed bag for the determination of physical and chemical properties. The Box-Behnken experimental design was used in the experiment. A total of 17 groups of pelleting experiments were designed with aged paddy rice replacement ratio, the conditioning temperature and the conditioning time were used as independent variables, and the feed pellet durability index, pelleting rate and power consumption per ton were used as dependent variables. A pellet mill was used in the test, and the diameter of the die hole was 3 mm and the length-diameter ratio was 10:1. When the process parameters of the conditioner and pellet mill were qualified and stable, the pellet feed samples were taken and the working parameters in the production process were recorded. The physicochemical properties of mixed powder such as angle of repose, angle of frictional, bulk density, tap density, compressibility, water absorption index, water solubility index, swelling power, viscosity characteristic value and pelleting characteristics such as pellet durability index, pelleting rate and power consumption per ton were measured. The three independent variable parameters were optimized and predicted. The results showed as follows: 1) With the increase of the proportion of aged paddy rice replacing corn, the angle of repose and the angle of friction, bulk density and tap density decreased significantly (P<0.05); the water absorption, peak viscosity and holding viscosity increased first and then decreased, and the pasting temperature and final viscosity increased significantly (P<0.05). 2) With the increase of the proportion of aged paddy rice replacing corn, the pelleting rate first increased and then decreased, and the power consumption per ton gradually increased, and the pellet durability index gradually increased (P<0.05). With the increase of conditioning temperature, the power consumption per ton decreased first and then increased significantly (P<0.05). The pellet durability index first increased and then decreased gradually. With the extension of conditioning time, the pelleting rate gradually increased, and the power consumption per ton decreased first and then increased. The pellet durability index first increased and then significantly decreased (P<0.05). 3) The results of response surface variance analysis showed that the main order of effects of each factor on the pelleting characteristics was: the replacement ratio of aged paddy rice > conditioning temperature > conditioning time. 4) The optimization and prediction results of process parameters showed that with the increase of the proportion of aged paddy rice replacing corn, the adjustable range of conditioning temperature increased first and then decreased, and the conditioning time decreased first and then increased. The study shows that the use of aged paddy rice instead of corn in feed processing can significantly improve the product quality, but also increase the energy consumption of pelleting.