Abstract: In order to analyze the effect of rock mass strength spatial variation effect on the slope reliability，the theoretical variation function's spherical model，Gaussian model，index model are introduced to depict spatial variation of rock mass strength.Visual Basic is adopted to write the corresponding program to the model above，fitting with the on-site point load test data to get the related model parameters.Monte-Carlo random sampling method is used to get the stochastic distribution characteristic of migmatite strength parameters.BISHOP method is taken to analyze slope reliability to get the reliability index of models corresponding to different slitting width.The results show that the spatial variation of rock mass strength will make reliability index increase，and the reliability index increases with slitting width increase when slitting width is smaller than the correlated distance，when the slitting width is greater than the correlated distance，the reliability index decrease first and then increase with the slitting width increase.The variation and trend of reliability index of Spherical model are almost the same as that of Gaussian model，and all are under the index model.

Key words: Variation function, Spatial variation, Slope reliability, Geostatistics