Abstract: The new self-impact seal has been widely concerned and recognized by peer scholars and industry experts since its introduction. In this paper, the thermodynamic effect and flow field characteristics of the seal were analyzed, the mathematical relationship between the thermodynamic effect and the leakage was established, and the influence of working condition and geometric parameters on them were investigated. The results showed that the established leakage equation agreed well with the simulation results (the error is 7.59% at variable rotational speeds). The entropy increasing effect of the seal varied most obviously with the sealing clearance when sealing clearance h≤200 μm. The leakage was significantly affected by medium pressure and sealing clearance, but was largely independent of rotational speed. Along with the sealed medium flowing into the clearance, the temperature of the flow field was rising step by step, and reached the highest at the outlet. The outlet temperature increased with the increase of pressure and sealing clearance, and decreased slowly with the increase of the number of stages. The effect of rotational speed on the outlet temperature was small. The thermodynamic effect was the main reason for the sealing tightness, while the stream contraction effect and the friction effect also favored the conversion of kinetic energy to internal energy to some extent. Compared with the existing non-contact gas seals (clearance, spiral, labyrinth, dry gas seal, etc.), the gas permeability effect after the self-impact could be basically ignored. When the gas passed through the flow paths of the three-dimensional Tesla valve of the seal, the gas in the sealing cavity was divided into two paths, and ultimately impacted each other in the intersection area of each sealing stage, and the kinetic energy of the gas was gradually converted into thermal energy and dissipated by impacting step by step, which leaded to the increase of temperature and entropy. The impulse and devision between the streams created an impact blockage effect, strongest at the intersection position, which was also the key position of pressure energy (kinetic energy) converting into thermal energy, and at the same time, the gas flow through the position was exceptionally intense. The gas flow rate in general tended to decrease due to the thermal dissipation after the impact. How to relieve pressure, control temperature and select the appropriate high-temperature resistant materials was the key to the new seal as soon as possible to realize the industrialization of the application.