Abstract: The shock wave and detonation gas of near field underwater explosion are investigated experimentally and numerically. A spherical TNT charge of radius 35mm is detonated in a 800 mm×800 mm water tank. The framing & scanning ultra-high-speed photography system is applied to obtain the trajectories of shock wave and detonation gas in its initial 80 microseconds. The arbitrary Lagrangian-Eulerian (ALE) method using LS-DYNA software is applied to simulate the processes of close-proximity underwater explosion for varied spherical charges. Comparisons with the experimental tests verify the results of numerical solutions. The engineering formulas of velocities and pressures for shock wave and detonation gas are proposed.