Laser-induced plasma formation and shock wave generation mechanism are our concern problems in investigating high intensity laser pulse focusing into water. A high speed schlieren photography technique with double-pulse lasers is used as a background light source, and the temporal and spatial evolution of shock wave are obtained. A two- phase computation model is established in consideration of water vaporization, plasma absorption laser pulse energy. The processes of laser induced plasma shock wave in water are numerically simulated. A reasonable agreement is obtained between experimental and simulation results. The shock wave propagation characteristics are studied，and comparison between simulation results and theoretical predictions are presented. The results show that the shock wave speeds in the initial stages of laser induced breakdown in water is up to 5 km/s, and pressure is up to a dozen GPa. Shock wave velocity and pressure decay rapidly over time, which decrease to acoustic speed in an 1 μs later after breakdown.