Geostress measurement is a direct and effective way to get initial geostress. But initial geostress is disturbed in drilling, it exists the phenomenon of stress relief and stress redistributing after drilling, that makes the measuring value different from the actual value of the initial geostress. In this paper, the process of geostress measurement in borehole is simulated by using finite element method, the effects of rock property, stress border and fractures on geostress changes are studied, and the sensitive factors to initial geostress changes are summarized.