In view of the advantages of high utilization of optical energy and easy field of view broadening, Mach-Zehnder interferometer (MZI) has a wide range of applications in optical filtering, frequency discrimination, and so on. However, in practical applications, its spectrum will be affected by various factors, resulting in performance degradation. In this work, the theoretical expressions of MZI interference spectrum are derived considering the influence of divergence angle 2θ0 and spectrum width Δν of incident light, and then their influence on MZI spectrum is analyzed quantitatively. The results show that the larger the optical path difference l of MZI is, the more significant the influence of Δν on its spectrum is, and the greater the ratio of lto incident light wavelength λ is, the more significant the influence of θ0 on its spectrum is. When λ=355 nm and l=3 cm (the first case), Δν=10 GHz and θ0=4.5 mrad will reduce the fringe contrast K to 2.8% and 16.3%, respectively. And when λ=532 nm, l=59 cm (the second case), Δν=0.5 GHz and θ0=1.25 mrad will reduce K to 3.2% and 15%, respectively. In order to reduce the influence of the beam divergence angle, the prism field broadening technique is further studied theoretically. The results show that if the thickness d and refractive index n of the compensation prism meet the conditions of d=nl/(n-1), in the first case, K is still higher than 93.1% when θ0=50 mrad, and K will drop to 33.3% even when θ0=70. In the second case, K is still higher than 94.0% when θ0=25, and K will drop to 37.6% when θ0=35 mrad. If d takes different optimal values according to different θ0, in the first case, K is still higher than 92.1% when θ0=70 mrad. And in the second case, K is still higher than 94.4% when θ0=35 mrad.