Abstract: A new developed transient simulating device is firstly used to measure the roughness in a typical field, and then using this roughness as input signal to study the relationship between the input and the output, the working performance of the machine on the simulating device in laboratory. The developed transient simulating device consists of a comparator, an amplifier, a director motor (speed adjustable) and a transmission device which converts the rotatory motion of the motor to up and down motion of a rod. The rod, simulates the roughness with up and down motion, pushes or pulls the wheels of the machine. Through measuring the vibration of the working unit of the machine , the relationship can be obtained. The results show that the field roughness, commonly, is a signal with low frequency (<10Hz) and large vibration amplitude(<100mm). The developed device has a high simulating precision.