Abstract: In order to achieve precise control for sowing spacing, this seeder was designed based on crank rocker mechanism and infrared detection. Variable spacing seeder was based on crank rocker mechanism, and changed the sowing spacing by changing crank length which was controlled by stepping motor and screw rod. The model between transmission ratio of seeder and sowing spacing was achieved, and then the model between stepping motor angular displacement of variable spacing seeder and sowing spacing was achieved, so the sowing spacing was controlled.Monitoring system of sowing distance was achieved by two sets of infrared sensors. The falling interval between two adjacent seeds Δt was tested, and then the sowing spacing was calculated with speed of planter. The infrared detection system and sowing spacing control system were tested, the result showed that the range of detection rate was 97% to 99%, the range of pass rate for sowing spacing control system was 96% to 91%, and the range of coefficient of variation was 6.2 to 13%.