The computational method of fluid dynamics and discrete element method were used to study the air-solid flow of a fertilizer air mixing chamber in a synchronous deep fertilization unit. In this model, the fertilizer particles were simulated by EDEM software, and the gas phase was demonstrated by ANSYS Fluent software. The movement rule of gas and fertilizer was analyzed by studying the influence of throat area, throat length, gas inlet pressure and fertilizer removal rate. The simulation results showed that the cross-section performance of the gas-fertilizer mixing chamber with type 2 throat was good, the pressure loss in the throat was small, and the air velocity was the fastest. The throat area and the fertilizer particle flow entrance pressure mainly affected the airflow velocity and the axial speed of the mixing chamber. The movement of fertilizer particles was less affected by mixing throat length and feed rate of fertilizer. The increase of throat cross-sectional area led to the decrease of airflow velocity and pressure loss in a certain range. With the increase of air inlet pressure, the resultant force and velocity of fertilizer particles were increased, and the suitable inlet air pressure was from 450Pa to 550Pa. The results showed that the CFD-EDM coupling method was reliable as an analytical tool for understanding the movement of fertilizer particles in airflow field, and the numerical simulation of fertilizer particle movement based on CFD-EDM coupling method can provide a theoretical basis for the development of rice lateral deep fertilization device. It had guiding significance for the optimization and improvement of the existing pneumatic rice fertilizer applicator.