A hydraulic sleepless speed system was proposed for a bivariable fertilizing application based on PLC, in order to enhance the stability of the hydraulic sleepless speed system and eventually achieve precise fertilizing. With particular emphasis on the stability of the hydraulic circuit and the actuation control method, mathematical model and simulation model for hydraulic sleepless speed system were established. More specifically, hydraulic sleepless speed system with stable oil circuit and oil pressure sensor was designed to ensure hydraulic system stability, while PID control algorithm was employed to compensate transmission error according to the mathematical model. The hydraulic sleepless speed system was then simulated in different PID control parameters. Simulations show that the results are reasonable and applicable, providing some theoretical guidance to the characteristics anticipation and test of hydraulic sleepless speed system. It is also found that when the PID parameter is chosen as Kp=10, Ki= 0.08, Kd=8, the fertilizing precision will be satisfied.