Centroid anisoplanatism degrades the precision of tip-tilt disturbance measurement and therefore the performance of beam jitter control. In this paper, the arisen of centroid anisoplanatism is explained by Zernike-polynomial expansion in Cartesian coordinate, which focuses on the cross coupling between tip-tilt term and coma term. To our knowledge, this interpretation is significantly different from previous research. The simulation of beam jitter control in presence of centroid anisoplanatism is accomplished. The larger residual variance of tip-tilt disturbances after correction can be found due to centroid anisoplanatism.