In the study of diffraction field calculation of spatial curved surface light source, it is a popular algorithm that considering the curved surface light source as a set of small triangle surface light sources. The analytic expressions of arbitrary triangular surface light spectrum and special frequency point is derived based on coordinate affine transformation. The problem of partial triangular spectrum loss in the traditional method is solved and the quality of the reconstructed image of the hologram is improved. Through rigorous theoretical analysis and calculation, the analytical expressions of two-dimensional and three-dimensional arbitrary triangular spectrum is solved accurately. The analytical expression of three-dimensional primitive triangular spectrum is simplified. A fast calculation method of 3D objects computing holograms using surface element division is obtained. Theoretical simulation and experimental results verify the validity of this method.