Abstract: In order to make the quality of fringe spacing and fringe visibility of interference pattern to meet the strict demands of active coherent laser detecting system of far distance, the distribution characteristics of coherent Gaussian beams based on Mach-Zehnder interferometer were analyzed. Optical intensity distribution of coherent Gaussian beams was deduced. Then interference pattern of scanning coherent Gaussian beams was gotten. The expressions of optical path difference, fringe spacing and fringe visibility based on Mach-Zehnder interferometer were derived by physical optics theory. The influences of rotation angle of beam splitter, detection distance and scanning speed on distribution characteristics of coherent light of far distance were analyzed and simulated numerically. As a result, the quantitative relation of rotation angle of beam splitter, detection distance and scanning speed was found. The results show that the distribution of coherent light of far distance is mainly controlled by rotation angle of beam splitter, detecting distance and scanning speed etc. Rotation angle of beam splitter in the interferometer has the influence on both fringe spacing and fringe visibility. The conclusion is helpful to choose the rotation angle in the experiment. Fringe spacing and fringe visibility should be taken into consideration simultaneously and the rotation angle of beam splitter is adjusted. It's useful to make the fringe visibility as large as possible.