A wavefront analysis method of pinhole point-diffraction based on waveguide theory is proposed in this paper. In this method, the pinhole is treated as a circular waveguide and the modes in the waveguide are calculated by analytical method to acquire the electric field distribution at the back surface of the pinhole. Next, diffraction wavefront in the far field is derived by the vector diffraction theory. Finally, the pinhole transmittance, the intensity and the phase of the diffraction wavefront are analyzed in detail. Results show that the boundary conditions of the waveguide cause the rotation asymmetry of the electric field components at the back surface of the pinhole, and then introduce the astigmatism aberration into the diffraction wavefront. In order to make the transmittance larger than zero, the pinhole diameter must be greater than 0.6λ to ensure that the modes in the pinhole meet the waveguide transmission conditions. The difference of the amplitude distribution between two electric field components in diffraction wavefront leads to rotational asymmetry of the intensity of the diffraction wavefront, while the difference of the phase distribution makes the diffraction wavefront elliptically polarized. Simulation results obtained in this method provide vital reference for the design of the pinhole structure in the point-diffraction interferometer.