Research conclusions :Through analysing the principle of probobility integral deeply and summing up the experience，a new kind of probability distribution model (the asymmetric possibility distribution model) is presented according to the characteristics of the random medium theory． The relation between the probability distribution model and major influence radius r is analyzed． With the increase of the mining depth ，the variation of the negative exponential function by section occurs to the r value． Taking the calculation parameters of the probability integral and the face subdivision method as breakthrough point ，and according to the occurrence characteristics of large inclination of inclined coal seam，it is put forward that subdivising the face along its strike can effectively correct the idealized defects of the probability integral model． The calculation example proves that this method can effectively improve the accuracy of the deformation prediction for railway － underlying goaf． It plays a positive guiding role in the railway alignment ， railway design and goaf disposal．