In this paper, numerical simulation and experimental verification methods are presented to investigate the influence of nonparallel slot and double-prism ridge in observing clear interference fringes. This result is essentially in the Fresnel double prism interference experiment using a line source. Initially, the interference intensity distribution formula of the Fresnel double prism on the observation screen is theoretically obtained. This is accomplished using geometrical optics and the principle of interference. In addition, the visibility of the interference fringe as a function of the angle between the slot and the ridge is obtained using numerical simulation. Theoretical analysis shows that as the angle increases, the interference visibility falls, then rises, and then falls again. Finally, an attempt to experimentally verify the theoretical results is also presented. The experimental results seem to be consistent with the numerical simulation results.