Abstract: Hydrodynamic wake is one of the important physical fields for the non-acoustic detection of submarines, and its accurate prediction is difficult due to the complexity of the marine environment. The Volume of Fluid (VOF) method is used to numerically simulate the stratified flow field of a submarine under direct navigation, and the influence laws of the speed, dive depth, and seawater stratification on the free-surface wake features and internal-wave wake features are obtained. Canny edge detection operator theory is applied to extract the wake profile features, and the wake angle and transverse wave tensor angle are measured. The results show that the submarine's wake does not present a typical "V" wave when the Fr number is low at a large dive depth, but gradually changes from a "spot" to a parallel wave with the increase of the Fr number, and eventually evolves into a distinct "V" wave. The strong stratification of seawater enhances free-surface perturbation, making the free-surface wake characteristics more pronounced. These results provide a basis for image recognition of hydrodynamic wake characteristics of submarines.