Mechatronics system is widely used in computer numerical control, robots, medical equipment, and automatic production etc. Whereas the frequency responses of sensors and actuators in mechatronics system vary greatly, and then sampling time is also different among some links of mechatronics systems. This paper presents the multirate nature of mechatronics systems based on the characteristic of sensors and actuators. Then mechatronics system is described as a multirate discrete control system. Mathematical model of the system is established using lifting technique. Finally, a kind of motion control system that includes multirate controller is analysed and simulated with the different three sampling rates separately. The results show that the presented multirate discrete control system really exists in mechatronics system, and the performance is also influenced in a certain extent under traditional control method.