Abstract: The parameter of light source can influence greatly on the processing ability of water jet guided laser. Aiming at the selection of light source, a physical model was established to describe the interaction between laser and water so as to expand the application field of water jet guided laser processing. The evolution of free electron density in the focus region of laser under different pulse durations and wavelengths was simulated based on a Runge-kutta method. The influence of physical processes such as multiphoton ionization, avalanche ionization, electron diffusion and recombination on the free electron density was investigated. The theoretical breakdown thresholds of water with different laser parameters were determined, and the corresponding verification experiments were carried out. On these bases, using appropriate laser source, a water jet guided laser processing was carried out for 304 stainless steel. The results show that the application of proper laser source can be beneficial for promoting the coupling efficiency of laser and water jet and reducing the coupling loss as well as suppressing the generation of thermal defects, consequently can provide high processing quality.