Abstract:Generally,underground sedimentary stratum consists of several kinds of rocks,with very strong anisotropy and different mechanical property. Moreover,during evolution,the difference of depth,temperature,confined pressure,and the influence of filling,degradation,which probably happened after the fracture forming,make the mechanical property of underground sedimentary stratum changed. The cracking of underground sedimentary stratum is also multiphase in the course of geological history. All these characters of underground sedimentary stratum make it difficult to forecast the distribution of fracture. According to all these characters,comprehensive quantitative method is used to establish mathematic model,analyze the influent factors of cracking,and determine the parameters of model and the steps of modeling. Then the fracture developing probability and fracture characters are predicted. At last,a sample is introduced taking from petroleum industry.