Laser Doppler velocimeter (LDV) is widely applied in the measurement of fluid velocity with the advantages of high accuracy, non-contact measurement and quick dynamic response. The fringe nonuniformity is a key factor to influence the measurement accuracy of LDV. To accurately measure fluid velocity of LDV, the interference fringe spacing and the gradient distribution in the measuring volume have to be determined exactly. The interference fringe spacing and the gradient distribution of LDV in the measuring volume are analyzed in theory. The relationship between the Gaussian beam propagation characteristics and its interference fringe distribution are revealed. The parameters influencing the interference fringe distribution are determined. The beam waist radii of the green beam and purple beam are 114 μm and 83 μm respectively, which are obtained by beam profiler. Meanwhile, the spatial location of the beam waist is determined. The interference fringe spacing and gradient distribution of green and purple beams in the measuring volume at any locations are quantified by using measured parameters. In the measuring volume of green and purple beams, normalized fringe gradient maximums can reach 0.46% and 0.60%, respectively. The interference fringe spacing results of green and purple beams measured by spinning-disk system are compared, and theoretical analysis and measuring results of the interference fringes distribution are verified. The maximum relative errors are 0.87% and 0.78%, respectively.