Studying the buoyancy diffusion laws and infrared characteristics on the water surface of submarine thermal wake is of great significance for submarine infrared detection. The submarine scale-down model was taken as the research object, and the three-dimensional calculation model of submarine thermal wake was established. The numerical simulation of the buoyancy and diffusion process of submarine thermal wake was performed by using the overset grid, Volume of Fluid(VOF) model method and the flow-through method separately. The buoyancy and diffusion law and temperature field characteristics of submarine thermal wake were analyzed. Through experimentally measuring infrared thermal image on water surface and the buoyancy and diffusion images of thermal wake, the accuracy of the two simulation methods was verified. The results show that the methods based on overset grids and VOF models are more accurate, the time deviation of maximum thermal wake temperature is 0.2 s and the temperature deviation is 0.003 K. It can well simulate the buoyancy diffusion and temperature distribution characteristics of submarine thermal wake.