Abstract: Because of the model error and the error of soil mechanics parameters, traditional planar frame model cannot exactly reflect the general situation of displacement of the pit. In order to improve the accuracy of the calculation, an improvement method is proposed by modifying the computational mechanics parameters of the soil. They were determined by taking the positive back analysis process. A radial basis function neural network and the compatible space computing model was introduced to take the back-calculation process, It is proven that the result is more accurate than the result of the traditional method.