Abstract：The low-permeability and impermeability of the stratum are hot issues for oil shale in underground mining，so it is of vital significance to form permeable belts among various mining shafts，while the thermo- chemical functions during oil shale heating are prerequisites of forming the permeable belts. Based on the problems mentioned above，the oil shale thermoelastoplastic damage model of heterogeneous medium is established；and then a systematic method of defining damage variables is given. Further，the material parameters of thermal expansion coefficient，thermal conductivity，specific heat，elastic modulus and tensile and compressive strengths are used as the random variables of satisfying Weibull distribution；and the parameters of numerical calculation is given in Matlab with Monte Carlo method. In addition，numerical simulation of thermal cracking during the process of heating in oil shale in underground mining is performed. The results indicate that the different thermal expansions and elastoplastic properties and distributed randomness of various mineral particles composed of oil shale will lead to the nonuniformity of thermal field，deformation field and stress field in heating process，which makes the particles of oil shale deform incompatibly；and the release of product pyrolysis results in irreversible damages of oil shale material and structure. These are the main reasons for the thermal fracture of oil shale. When oil shale is heated through thermal conduction，temperature transfers slowly，so the spacing between heating well and production well should not be kept too long. When difference exists in oil shale reservoir¢s properties，heating well should be chosen in the high conductivity region. Oil shale¢s stratification is vital for developing permeation zone in in-situ retorting. Oil shale will generate additional expansion force as it reaches its pyrolysis temperature，and stratification will be cracked first，so the oil shale stratification should be utilized to enhance its permeability.
