The jet mixing apparatus (JMA) is an important part for mixing the water with the pesticide, which has good prospect in large plant protection machinery. The parameter of area ratio, area of nozzle and distance between nozzle and mixing chamber were discussed by theoretical analysis. The standard k—εtwo-equation model was adopted to simulate the interior flow field. Combined with experiment data, the performance characteristics, the effects of structural parameters on the JMA property were discussed. Results showed that the optimum area ratio was related to working pressure, outlet pressure and jet pressure. The distance between nozzle and mixing chamber should be equal to optimum extent of free stream. The maximum relative error and average error of relative pressure at different area ratio were 0.125 and 0.051, respectively. The numerical model and simulation method were validated validate to meet the requirements of engineering. The jet flow decreased when the relative pressure greater than 0.3. The maximum relative pressure was between 0.5 and 0.6 under different available pressures. The optimum area ratio of JMA was between 1.6 and 2.0. The optimum distance between nozzle and mixing chamber was between 2.6mm and 4.6mm.