Burning surface calculation is an important item in solid rocket engine design. In order to accurately calculate the parameters such as burning surface change law in the combustion chamber, the level set based method is used for burning surface calculation, firstly, the complex burning surface is divided into a uniform grid by voxelization; then the distance transformation method is used to calculate the signed distance function, and finally the information of the contour surface in the grid is obtained to generate the burning surface change curve. The comparison with the CAD method shows that the relative root-mean-square error of the method used in this paper is within 2% with the numerical calculation results.