Fabry-Perot interferometer(FPI) is an optical instrument with important scientific and practical value, which can be widely used in optical frequency discrimination, optical frequency locking and spectral measurements of the hyperfine structure. However, in practical applications, the spectral characteristics of the interferometer are affected by many factors. In this article, the impact of several factors on Fabry-Perot interferometer spectral properties, such as the beam divergence angle, the spectrum of the incident light, the absorption loss, surface defects and non-parallelism of the interferometer two plates were studied in depth. Considering the above practical factors, a general expression for the transmission spectrum function of F-P interferometer was derived theoretically. The overall shift of the transmission spectrum caused by the divergence angle was given quantitatively. The concept of equivalent spectral width of the emitting laser was proposed, the broadening effects on the transmittance spectrum of the incident beam divergence angle, the spectrum of the incident light, surface defects and non-parallelism of the interferometer two plates were all considered, and their quantitative equivalent formula was given. These results would provide a reference for the design and application of Fabry-Perot interferometer.