Abstract: Although it is well known that the stability of concave slopes in plan view is better than that of straight slopes, it is difficult to accurately calculate the factor of safety of concave slopes because the lateral forces perpendicular to the sliding direction have an effect on the stability, but there is no suitable method to calculate them. For the sake of simplification, the existing studies calculate the lateral forces by treating that they are active earth pressures. In order to verify the rationality of that treatment, the lateral forces are regarded as the values of active, static and passive earth pressures respectively. Based on the Spencer method, the method for calculating the stability of a concave slope is deduced considering the lateral forces. And then the calculation program is compiled by using the Matlab software to analyze the difference of factor of safety of the concave slope under three different soil pressures. The results show that by considering the lateral pressure as the earth pressure or the static earth pressure, the stability of the concave slope is even lower than that of the straight slope. When the lateral pressure is considered as the passive earth pressure, the factor of safety is significantly larger than that calculated by the finite difference software Flac^3D. Therefore, it is unreasonable to simply regard the lateral pressure of the concave slope as the earth pressure as the active, static and passive earth pressures. How to calculate the lateral forces of the concave slope is still a problem to be further studied.