Abstract: There’re several factors affecting the accuracy of terrain correction to obtain geoid with centimeter-level: accuracy of DEM,resolution and the integral radius. Derive the linear relationship between DEM and terrain correction by computing the spherical harmonic expansions. The result showed that the accuracy of DEM should be better than 81m. After the relationship between resolution and the degree of spherical harmonic expansions and integral radiusanalyzed, the best suitable factors for geoid with centimeter-level was giant.This article chosed different resolution and different integral radius to compute terrain correction with DEM of Tibet. The test results showed that the resolution of 6″ DEM could meet the needs of geoid with centimeter-level. And it needs 50’ integral radius to meet the corresponding requirements.