Abstract：There are a lot of blind application of chemical fertilizers in the planting of bananas, which leading to waste of fertilizers and environmental pollution. According to the distribution pattern of banana root system, a variable fertilizer apparatus was designed in this paper. Based on the image processing of banana root morphology and the statistics of the area area pixels, the distribution pattern of the banana root system in the horizontal direction was analyzed. Based on the characteristics of the root area distribution, the change of fertilization amount along with the root distribution in horizontal was normally distributed, that is, the amount of fertilizer in the main root was the largest. Based on this, a rotary plate variable fertilizer apparatus was designed. By calculating the fertilizer amount distribution discharged on the simulated ground by the simulated fertilizer discharger, it was determined that the distribution law of the fertilizer amount along the forward direction of the machine was also normally, which was the same with the banana root distribution. In order to ensure that the fertilizer discharging amount and the center position of the normal distribution of the root are consistent in space, taking the spatial consistency of the center positions of the two normal distribution as the goal, the operation process planning was carried out for the image acquisition interval time, algorithm time, motor response time, fertilizer falling time, etc., and the accompanying operation control model of the machines was established. The variable control system was used to achieve and ensure that the center positions of the two normal distributions were consistent in space. The center combination simulation test was carried out with the movement speed, the moving period of the rotating plate, the central angle of curved slot and the opening size of curved slot as independent variables, and the length of fertilizer distributing and the fertilizer discharge amount were used as test response values. The result of optimal parameter combination was that the movement speed is 0.25 m/s, moving period of the rotating plate is 10.00 s, the central angle of curved slot is 90.00°, and the opening size of curved slot is 20.00 mm. The model and test errors, simulation and test errors of the length of fertilizer discharge are 4.98% and 3.30% respectively, the model and test error, simulation and test error of fertilizer discharge amount are 11.15% and 6.68%, respectively. The field test was conducted to examine the field operation effect of the fertilizer discharger, the average qualified rate of fertilizer discharging length was 96%, the average qualified rate of fertilizer discharge amount was 95.33%，the operation performance of fertilizer apparatus was good.