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It has been widely recognized that rice seedlings made from biomass such as crop straw and wood chips can reduce white pollution, realize resource utilization and raise seedling quality. At present, biomass forming mainly adopts compression molding, which has problems such as high energy consumption, low productivity and poor molding quality. The problems mentioned are solved effectively by pneumatic method. The object was to optimize the airflow distribution chamber of pneumatic forming machine and improve the production quality of rice seeding-growing tray. The reasonable air distribution chamber structure was precondition for normal operation of pneumatic forming machine for rice seeding-growing tray. Based on the gas control equation, fluent software FLUENT was used to simulate the air flow field to ensure a uniform flow field structure in the airflow distribution chamber, and produce qualified rice seeding-growing tray. Combined with orthogonal test design and numerical simulation technology, the single factor and orthogonal simulation test of airflow field were carried out with thickness of the cavity, vent diameter, base angle of cavity as experimental factors and speed unevenness coefficient as assessment consumption. The experimental results showed that the best parameters in combination were as follows: cavity thickness of the airflow distribution was 110mm, vent diameter was 15mm, base angle of cavity was 0°, vent air velocity was within the range of 0.09~0.14m/s, nonuniform coefficien was 11.37%, flow velocity was stability, and distribution was uniform in airflow distribution chamber. The mean relative error between the simulation results and the measured results was 1.59%, bilateral correlation coefficient was 0.028, and there was a significant correlation. The forming rate of rice seeding-growing tray was 92.3%, the variation coefficient of hole weight and under surface thickness was 10.2% and 9.81%, respectively, which met the production requirement. The research result was of great significance to improve the molding quality and molding efficiency of the pneumatic forming machine, which can provide reference for the optimization design of similar structure moulds.