This study focuses on the analysis of steering angle changing under fatigue driving on a driving simulator. Monotonous expressway environment was designed as the simulating scene. 14 drivers were invited to attend the simulating experiments. Speed, steering angle and time were sampled on real time at frequency of 8Hz. Analysis were based on data selected from 3 different alignments road sections. The analysis result showed that the absolute mean, standard deviation and energy of steering angle were rising when fatigue deepening and these trends would minish the differences of indices causing by different road alignment.