Vortex around ships is easy to cause noise, vibration and fatigue of propellers. In addition, the complexity and variability of vortex will also have a greater impact on sensors and detection equipment installed on the surface of the vehicle. It is necessary to carry out corresponding research. In this paper, the fluctuating pressure was numerically analyzed using improved DDES model. And applying overset grids to better capture vortices around submarine sail. The numerical study of a three-dimensional unsteady vortex structure was performed for calculation. There were two vortex tubes and some broken small vortices behind the sail. The simulation results showed that trailing vortices behind sail slightly swept up and the distance between two vortex tubes became larger.