The circulating cooling water of the underwater vehicle power system discharged from the discharge port, mixed with the environmental water for heat exchange and formed the thermal jet. The thermal jet diffused and floated in the environmental water and forms infrared characteristics on the surface of the water. In order to explore the influence of the structure of the discharge port on the infrared characteristics of the underwater vehicle thermal jet, this paper used the method of simulation analysis and experimental verification. Based on the CFD calculation software platform, the motion model of underwater vehicle was established, the structure of different radius-ratio oval discharge ports was designed, and the infrared characteristics of thermal jet were compared. The influence of the radius ratio of the oval discharge port on the infrared characteristics of the thermal jet was verified by the scale tank experiment, and the authenticity of the simulation calculation method and design parameters was verified at the same time. On the basis of oval discharge ports, the number and distribution position of discharge ports were further designed to suppress the infrared characteristics of thermal jet and improve the thermal stealth performance of underwater vehicles. According to the simulation calculation and experimental results, under the condition of the same discharge flow, the smaller the radius ratio was, the better the mixed heat transfer effect of the oval discharge port was, and the less obvious the infrared characteristics were. At the same time, increasing the number of discharge ports and adopting the symmetrical arrangement of discharge ports could further strengthen the temperature attenuation of thermal jet and reduce the surface maximum temperature.