The utility model relates to a water pressure type underwater ignition device. The water pressure type underwater ignition device is mainly technically characterized by comprising a gland, a sealing ring I, a piston, a striker spring, a firing pin, a guide screw, a sealing gasket, a moving body, a sealing ring II, a stab detonator, a booster pellet, a detonating tube, a moving body spring, a body seat and a safety pin, wherein the gland, the sealing ring I, the piston, the striker spring and the firing pin form a firing mechanism of the device; the guide screw, the sealing gasket, the moving body, the sealing ring II, the stab detonator, the moving body spring, the body seat and the safety pin form a safety mechanism of the device; the booster pellet and the detonating tube form a booster mechanism of the device; the striker spring and the moving body spring are in a non-energy storage type natural extension and contraction state after being assembled. The device has the characteristics of simple and reasonable structure, low manufacturing cost, function reliability and the like.