Based on the multi beam interference principle, the intensity expression of the transmitted beam for a Gaussian beam striking obliquely through a nonparallel Fabry-Pérot interferometer has been derived. According to that, the influence of the nonparallelism in Fabry-Pérot interferometer mirrors alignment at a different tilted angle and waist radius on the transmission of a Gaussian beam has been investigated theoretically. The results show that the incident angle and the nonparallelism in Fabry-Pérot interferometer mirrors alignment have important effect on the intensity distribution, the peak intensity and the position of the peak intensity of the transmitted beam; the diffraction effect of the Gaussian beam must be considered when the waist radius of beam is small or the facet reflective index of the Fabry-Pérot interferometer mirror is large; if the wedge angle is negative, the intensity of the transmitted beam will reduce quickly to zero at the recoil position, which can be used to measure accurately the distance.