In order to realize the positioning and quantitative fertilization of maize in seedling stage under farmland environment, a control system was designed, which was based on machine vision to position and fertilize maize in seedling stage and improve fertilizer utilization rate. The control system controlled the maize positioning fertilizer applicator to travel in the field through the self-driving crawler. The fertilizer applicator realized intermittent fertilization according to plant location by using the structure of slice fertilizer discharger. After collecting the images of maize canopy at seedling stage, the area of maize plants at seedling stage was small, and there were many collected images without maize. In order to solve the influence of the above problems on operation efficiency and accuracy, the system used color features to distinguish a large number of background images and misrecognized plant centers during continuous shooting. By adding image preprocessing and algorithm post-processing, the method of plant center recognition and location was improved; in order to solve the problem of fertilizer lag caused by fertilizer falling time, system response time and positioning error, the compensation model of fertilization lag error was established, the relative distance of fertilization was calculated in real time, and the time of fertilizer falling was calculated accurately, which improved the control precision of intermittent automatic positioning fertilization according to plant. After experiment and verification analysis, the improved plant center location recognition method obviously reduced the image processing time and improved the robustness of the algorithm; according to the amount of single fertilization, the fertilizer applicator was set three gears (7.25g, 14.5g and 21.75g), and the coefficient of variation of fertilization stability, which represented the stability of fertilizer application per plant, was 1.93%, 1.87% and 1.93%, respectively. The control precision of the actual fertilization amount and the target fertilization amount of the fertilizer discharger was more than 95%. The average error of the distance between the actual fertilizer drop point and the target drop point can reach 3.2cm, which met the basic operation requirements of location fertilization. The fertilization control system designed can realize the quantitative fertilization according to the location of maize plants at seedling stage, and achieve the purpose of reducing application, improving quality and scientific fertilization.