Abstract: In order to reduce the seeding absent of seed drill, ameliorate the quality of mechanical work and improve the level of automation, the automatic reseeding monitoring system of seed drill was developed, which was based on single chip microcomputer AT89C51, the core of monitoring system. The monitor program was written by assemble language, while the corresponding treatment circuit and the reseeding mechanism were designed. When technical trouble was occurred, the monitoring system could not only give an alarm by voice and light, but also start the small stepper motor to drive the reseeding mechanism to continue work until stop to be examined and repaired. Experiment results show that the length of seeding absence can be reduced to the minimum because the sensibility of monitoring system is only 0.3 s.