Abstract: This paper studies the stealth properties of sails on the water and underwater. Based on the high-frequency method, it compares the Radar Cross Section (RCS) features of the conventional straight wall sail and the advanced 3D sail. Using CATIA and MATLAB, the numerical simulation of the RCS characteristics of sails and the calculation of radar detection probability are conducted, and the influence of different distances and angle territories on radar detection probability is discussed. The results show that the stealth performance of the advanced low-3D sail is considerably superior to that of the conventional straight wall sail.