In this paper, we first analyze the two-step imaging process in optical holography, namely, wavefront recording and wavefront reconstruction. According to the relationship of the four diffraction components in the spatial spectrum of the off-axis digital holography diffraction process, the minimum angle is derived between the object light and the reference light of the off-axis digital holography. According to the sampling theorem, the maximum angle is derived between the object light and the reference light in off-axis digital holography. The mathematical derivation of holography algorithm is introduced based on these foundations. When off-axis digital holography is recorded and reproduced, CMOS is used instead of the traditional holographic dry plate for receiving the hologram, and which is saved as a digital signal, finally, the object image is reproduced by MATLAB simulation. The current Fresnel approximation reconstruction algorithm is analyzed and verified by simulation.