To further study the application of Gaussian laser beams in underwater communication and information detection and the characteristics of the transmission process in different seawater environments, in this study, the most-common terrestrial suspended sediment particles in seawater were taken as an example. First, Mie scattering theory was combined with the Monte Carlo method to establish a 520-nm Gaussian laser transmission model in seawater containing suspended solids, and the effects of particle groups with specific diameters and densities on laser transmission were studied. Second, the variation in the normalized received power with the initial divergence angle of the laser at different detection distances was analyzed. The research results indicate the following. 1) When the diameter and density of suspended sediment particles in the Mie scattering model are changed, thereby changing the extinction coefficient, scattering coefficient, and asymmetry factor set in the simulation, the received power of the detection target decreases exponentially with increases in scatterer diameter, density, and transmission distance. 2) Within a certain range, the change in the initial divergence angle does not affect the power of the receiving surface, and this range decreases with increases in the scattering coefficient and transmission distance. The research method used lays a theoretical foundation for further analyzing the changes in Gaussian laser transmission characteristics in seawater containing complex particle groups (suspended bubbles, planktonic algae, and suspended sediment) and provides reference for related engineering estimates.