Abstract: In order to investigate energy propagation characteristic and distribution of laser water jet (LWJ) inside the coupling jet, a space propagation model of Gaussian laser was established. The total reflection propagation of laser was analyzed with beam envelope method (BEM). The evolution rules of laser electric field were explored in water jet with different diameters. The laser energy distribution in different cross-section of coupling jet was obtained, and corresponding experiments were carried out with 50μm diameter to verify the simulation results. On the basis of specific laser electric field distribution of coupling jet, K24 alloy was selected for ablation tests by LWJ with different laser pulses. The results show that BEM could predict energy propagation and distribution inside the coupling jet with simulation, and the processing demonstrates a consistency with the same cross-section of coupling jet.