For cavitation collapse problem in the out-of-water progress of underwater vehicles, the cavitation collapse characteristic is analyzed by means of slender-body theory. Based on 2D axis-symmetric circular cavitation collapse model, the pseudo 3D cavitation collapse hydrodynamics model in thickness water layer is established. Carry out calculation analysis for cavitation collapse in out-of-water progress of underwater vehicle. The results of cavitation flows and velocity of the cavitation collapse show that the calculation results correspond well with the one of the test. It can provide some references to the analysis of the hydrodynamic characteristics on launch of underwater vehicles.