Abstract: This paper gives two methods to simulate a stress field in the reservoir. The first method is that some measured stress data and the model of a three-dimensional membrane element are used to detemine the far field stress boundary condition with a back analysis and thereby to evaluate the stress field in the reservoir. The second method is a direct interpolation to evaluate the stress field with a moving least square method. A feasibility of these methods are discussed in the paper. To use the methods we simulate the stress field of Sanjianfang reservoir in Shanshan oil field and obtain a lot of good results.