As one of the most widely applied technology at present, near-earth spectrum detection technology has been used in precise variable fertilizer applicator for rice and wheat. In order to improve fertilizing performance stability and control precision of variable rate fertilizer applicator, the discrete element simulation model of outer groove-wheel variable applicator was established. To achieve the optimal structure of outer groove-wheel fertilizer apparatus, the discrete element method (DEM) and EDEM 2.2 software were put into use to analyze and numerically simulate the fertilizing performance. The effect of different fertilizer apparatus structures and control strategies for fertilizing on the stability of variable fertilization was studied, and with bench test and field trial to verify the accuracy of simulation model. The results showed that the fertilization variability of improved apparatus was significantly decreased, and the standard deviation was decreased by 14.59g, the variation coefficient was reduced by 9.9%. When the control strategy of speed priority was adopted, as the groove-opening was 19.34mm, it had the optimum fertilizer stability of 1.09%. When the control strategy of groove-opening priority was adopted, as the rotary speed of groove-wheel was 55.75r/min, the minimal fertilizer variability was 1.85%. And compared with the verification test results, the errors were less than 8.87%, 9.52% and 5.50%, respectively, verifying the accuracy of simulation and analysis for particle movement process in agricultural equipment using the DEM. The study illustrated that the improved fertilizer apparatus could perfect the stability of fertilizer and satisfy the demands of precision variable fertilization.