On basis of extenics theory, this paper adds thought of statistics and forms a method which based on extenics analysis of probability statistics. Being taken as examples of Yanbian Prefecture and Helong City project, the appraisal stochastic elements are produced by means of simulating the corresponding factors for each object using Monte-Carlo in Matlab. Then the classical matter-element and extensional matter-element are set up for the stability of rock mass of slope and influence factor, and the possibility of objects are worked out by element and correlation function. The Class of rock mass of slope are determined by the statistics of possibility, and hence some reasonable proposals are put forward.