Based on the time series of GPS station coordinate in the international Earth reference frame (ITRF),we evaluate annual micro-behavior of strain field in Chinese mainland with the triangle method. The results show that the annual micro-behavior of strain field is divided into two parts by the north-south earthquake belt in the research region. The prevailing direction of compressive principal strain field is nearly consistent in the western region. From west to east,the direction varies from NS to NE. It is in accordance with the direction of the modern compressive principal strain field. This suggests that geologic deformation in western region was mainly caused by that India tectonic plate pushes the research region northward and the Siberia plate pushes it southward relatively. It is an inheritance of new tectonic motion. The prevailing direction of the compressive principal strain field does not exist in the eastern region .The annual biggest shear strain is different greatly in every grid-cell. The values varies from 4.13×10?8 to 7.0×10?10. By and large the annual biggest shear strain in the western region is bigger than that in the eastern re-gion. And so is the variation between any two consecutive biggest annual shear strains in the same grid-cell. The annual surface dilatation show that in most grid-cells of the research region the surface dilatation is in compressi-bility,and the variation between any two consecutive annual surface dilatation in the same grid-cell is small.
