95%。The ratio of the single seedings, which is effected by the coefficient of the absorbing seeds directly, is an important parameter. The purpose of this paper is to design the variable control system for precision magnetic drum-seeder. In order to enhance the sowing efficiency, the roller is made speed-down when it is absorbing seeds, whereas it is made speed-up when it has absorbed or is sowing seeds. The variable control system embodies a F2812DSP controller, a PS2 keyboard and a photoelectricity sensor. Experiment shows that the efficiency has been raised by 16% and the ratio of single seedings is over 95%, when the speed of absorbing seeds is up to 16 r/min and the speed of absorbed and sowing seeds is up to 20 r/min. 