The initial in-situ stress field is composed of the gravity field and the structural field. The form, combination, direction and magnitude of the structural motion actions is the key for inversion analysis of initial in-situ field. An inversion method of initial in-situ stress field is proposed in this paper. Fuzzy evaluation data-base to every variety of feasible plans and fuzzy membership function for every variety of feasible plans is established, respectively. A method using fuzzy evaluation is used to identify the form, combination and direction of the structural motion actions and the genetic algorithm is used to get the undetermined coefficients, then the initial in-situ stress field is obtained. The numerical results show that the method is very effective and feasible.