Abstract：We obtain the gradient for the changes of CQG2000 model, to meet the needs of height conversion between map sheets at different scales, analyze the change correlation of the variety of quasigeoid in the spatial domain. Firstly, we define the gradient model of CQG2000. Secondly, we calculate the gradient value of CQG2000 by the 3rd order finite difference weighted by reciprocal of squared distance to derive the error of the gradient and the azimuth. Finally, to analyze the change trend of national height anomaly in China, we use the gradient of CQG2000 model. The results show that the gradient value in the area east of 102° E is small, the change is soft, and the direction of azimuth is eastward; while in the area west of 102°E, the gradient value is large, the local change is abrupt, and the direction of azimuth has obvious trend changes locally. Some gradient diffusion and convergence centers exist in western regions, such as Xinjiang, Qinghai-Tibet, where there are great gradient varieties, and the maximum gradient value of 0.625 m/(′) is near Motuo.
