Abstract: Variable?rate fertilizer applicator is one of the most important machines of precision agriculture.Nowadays, the main machine for topdressing in rice is centrifugal disc distributor, and this machine has a better width, but has an unstable spread uniformity at the direction of working width, and most of them also cannot fertilize with a variable rate at the working width direction.In order to satisfy the needs of variable?rate fertilizer application in rice, and use less fertilizer to produce more yield, a pneumatic variable?rate fertilizer applicator for rice production, which used outer groove?fertilizer?wheel and pneumatic fertilizer spreader, was designed.Firstly, the simulation of the key components of the variable?rate fertilizer applicator was carried out to optimize the structure of the mixed joint and the air divider box under the following initial boundary conditions: the inlet gas velocity was 12 m/s, the inlet gas volumetric flow of air divider box was 0.03 m3/h, and all the testing components were under the same pressure in outlet and environment.The results indicated that the small keyhole structure not only improved the average pressure in air divider box and the uniformity of airflow dividing, but also promoted the fertilizer falling for mixed joint of air and fertilizer.Secondly, a series of testing experiments of the key components of the variable?rate fertilizer applicator were carried out to investigate the correlation between the rotating speed of fertilization wheel and the amount of fertilizer application under the following conditions: use the mixed joint with small keyhole structure, the inlet gas velocity was 12 m/s and the air divider box pressure was 110 kPa.The results showed that there was a significant linear relationship between the rotating speed of fertilization wheel and the amount of fertilization, and the correlation coefficient was up to 0.998.Adjusting the rotating speed of fertilization wheel could accurately adjust the amount of fertilization.In other words, it could achieve the purpose of variable fertilization by real?time control the rotating speed of fertilization wheel combined with the fertilization demand and the forward speed of fertilizing machine.The variable amount of fertilization could be reached in the range of 40-200 kg per hectare when the forward speed of fertilizing machine was 1 m/s and the rotating speed of fertilization wheel was in the range of 10-40 r/min.And the errors of fertilizer application amount for each fertilizer ejector′s outlet was less than ±5%, which basically reached the requirements of fertilization uniformity.Finally, the impacts of the fertilizer pipeline length and installation height difference on the fertilization outlet velocity and lag time were studied when the inlet gas velocity was 12 m/s and the air divider box pressure was 110 kPa.The results showed that the fertilizer pipeline length and installation height difference had a significant effect on the fertilizer ejector′s outlet velocity and fertilization lag time.Therefore, in order to minimize the influence of fertilization lag time on fertilization uniformity, the fertilizer pipeline length should not be too long, and it is also suggested that the fertilizer ejector′s outlet is not higher than the inlet in order to reduce the impact of installation height difference.This study provides a basis for further prototyping and optimization of the pneumatic variable?rate fertilizer applicator.