A sowing leakage monitoring and marking system for sugarcane planter was designed. Light curtain sensor was used to monitor sowing leakage. When sowing leakage was detected, marking device marked the position of leakage in the field with lime stone powder. Experiments were conducted respectively on test bench in laboratory and on planter in field. The results showed that the regression coefficient R2 was 0.991 between monitoring system and manual measurement. In field experiments, the mean of the error (Qp) between marked point and the position real happed in the starting point of sowing leakage was -83 mm. The mean of that error (Zp) in the terminal point of sowing leakage was -63 mm. The standard deviation of Qp and Zp were 216.1mm and 155.6 mm, respectively. The sowing leakage position marked by system could be used for artificial reseeding.