Abstract: In this study, we have simulated the water-air flow characteristics of an underwater self-excitation inspiration jet device using an Eulerian two-phase flow model and RNG k-? turbulence model, focusing on the distributions of internal pressure and water-air flow velocity of this device and its water-air mixing process in inspiration and non-inspiration cases. Experimental tests were conducted to examine its performance and the variation trends of its impact power and erosion effect. The results show that relative to the non-inspiration case, inspiration makes the internal pressure closer to atmospheric pressure and brings about longer jet cores and significantly greater velocity at the outlet of the lower nozzle. In the inspiration case, high air concentration occurs in the whirlpool regions outside of the jet core if air is fully mixed with water, and air content increases gradually from the core to whirlpool. And the impact power at the target center and in its vicinity is significantly higher than that of the non-inspiration case, explaining the fact that such a device has a gathering energy effect. Moreover, erosion volume and erosion depth increase dramatically while the area of eroded surface decreases slightly. Calculations of inspiration capacity and pressures at typical locations show good agreement with test results.