Abstract: About FLAC^3D numerical simulation of underground mining, it is very important to generate the initial stress field in the model correctly. Considering the actual project conditions, calculation model is often needed to be excavated and grouped many times, and in order to facilitate multiple excavation and grouping, it is possible to occur such a case that the angle between measured principal stress and model boundary is not a right angle when building a model. In order to study the method of generating the initial stress field in that case, the values of stresses acting on the model boundary are solved by the basic theory of the elastic mechanics’ special problem, as well as the directions of stresses acting on the model boundary are determined by the Mohr circle pole point method and the method of force equilibrium. And finally, the initial stress field is generated by using the quasi stress boundary control method, which supplemented by displacement boundary control. Each principal stress value and direction in the calculated balanced model are compared with the actual conditions. The value of principal stress in each elevation position in the model is almost the same as the actual value, and the orientation of each principal stress is also consistent with the actual orientation. Thus it is proved that the quasi stress boundary control method is correct and reasonable, which can provide reference for generating initial stress field under similar circumstances.