In order to improve the ease of operation, the fuel economy and the dynamic performance of an automobile, an automated mechanical transmission controlled by electronics has been developed. As the control of the clutch is stochastic, complicated and changeable, the realization of the optimum engagement schedule of the clutch is the most important technique in the system. This paper uses high-speed switching valves which are simple in structure, and the clutch is controlled by pulse width modulation (PWM), thus greatly reducing the cost. The paper analyses the linear range and wave error of the switching valve system (SVS) and gives a quantitative basis to the parameter selecting of the switching valve system. A regulator with good performance has been designed by simulation. The experiment results show that it has reached the expected requirements.