Maize hole fertilization synchronizing with seeding is an effective means to improve fertilizer utilization efficiency. To solve the problem that the relative position of seed and fertilizer could not be detected and controlled in real time with the present hole fertilization device, a maize automatic hole fertilization device was designed, and an automatic targeting at seed method based on planetary gear train was put forward. On the premise of the same seed distance and fertilizer distance, the phase difference between seed trays and fertilizer trays was adjusted in real time to realize the real-time control of the relative position of seeds and fertilizers during seeding. The influence of the advancing speed, the distance between the seed metering device and fertilizer discharging device and the spacing in the rows on the position of seed and fertilizer dropping was analyzed, the calculation method of the relative position of seed and fertilizer was obtained, and the automatic seed control algorithm of hole fertilization was designed. A control system based on STM32F103 was built, and the hardware system and software system were designed, seed and fertilizer dropping information was detected and controlled in real time. The experiment result showed that the average distance of seed and fertilizer was 8.6mm, 6.1mm, 11.7mm and 8.5mm, while the forward speed was 3km/h, 4km/h, 5km/h and 6km/h, respectively, which met the requirements of seed hole fertilization.