A speed control system for hydraulic motor is introduced,whose flow was adjusted through cartridge valve which controlled by the highspeed on/off valve.Its mathematical model based on the similar theory between the electronic and hydraulic system in the mathematical model was established to illustrate its speed control principle and to analyze the influence factors of speed controlling performance.A reasonable method to match every component parameter was put forward.In the end with the design and simulation analysis of the speed control system,the rationality of parameter matching and the different speed controlling performance with different parameter were verified.The conclusion shows:Speed control system with fast response,wide speed range has a large throttle loss under the low duty cycle,it should be ensured to work at the high duty cycle condition as far as possible.