The invention discloses a numerical analysis method for stability of a pole tower base on unsaturated expansive soil foundation. According to the method, firstly, a pole tower base model and an unsaturated expansive soil foundation model are created; secondly, corresponding material properties are set for the pole tower base model and the unsaturated expansive soil foundation model respectively; thirdly, correlative analysis procedures are established, grid partition is carried out on the pole tower base model and the unsaturated expansive soil foundation model, boundary conditions for constraining the displacement of the bottom and the periphery of the unsaturated expansive soil foundation model are set, and gravity load and corresponding load on the upper portion of the pole tower base model are applied; finally, operation is submitted, and an operation result is analyzed. The method easily and effectively solves the problems that the pole tower base of an electric transmission lineis deformed and the stability is influenced since the water content rate of the unsaturated expansive soil foundation is changed; the bearing force of the unsaturated expansive soil foundation after the water content rate is changed can be obtained, and the numerical analysis method is provided for determining the stability of the pole tower base on the unsaturated expansive soil foundation.