Abstract: The increase of integral emittance caused by Corkscrew motion in LIA is theoretically analyzed and numerically calculated in the paper. The simulation shows that the Corkscrew of beam centroid is a low frequency motion which overleaps the average eccentricity between centroid of beam and axis of accelerator and a dispersive effect. Although there are many common inspiriting factors, the Corkscrew motion and average eccentricity of beam centroid have absolutely different mechanism. The original inclined incidence and the energy spread of beam are the basic factors of Corkscrew motion. Magnetic field, magnetix axis tilt and assembly method influence obviously the amplitude and frequency of Corkscrew motion, and the growth of integral emittance. On the other hand, the eccentricity of beam cen