An electrohydraulic (E/H) steering control system was designed for tractors with hydraulic steering system. The hardware of system included a TMS320F2812 DSP (digital signal processor) and its interface circuits such as PWM (pulse width modulation) controller and others. The control algorithm adopted was PID (proportional-integral-differential) control with nonlinear compensation method. A TD654L type of tractor was taken as research platform mounted with proportional directional valve and angle sensor. Tests had been taken to identify the parameters of algorithms and implement automatic steering following guidance signal. The results of track test with guidance signal from guidance generator showed that the steering offset was less than 7% and the average of lag time was 0.15s. It provided a research base for automatic guidance.