Abstract: This paper focuses on the analysis of velocity changing rules when fatigue driving on a driving simulator.Monotonous highway environment is designed as the simulating scene,15 drivers are invited to attend the simulating experiments and 14 sets of effective data are collected for analysis.Velocity,acceleration,vehicle location and time are recorded at 8 Hz on real time.Data from 3 different road alignments are chosen for analysis and the analysis result shows that the velocity is higher when fatigue driving and the driver tends to easily exceed speed limit but it shows no obvious rules for velocity variation,and the standard difference of velocity is lesser and the differences are significant at the 0.05 level.The main frequency component of acceleration is transferred from lower to higher and spectrum amplitude and energy reduces evidently.