The invention provides a gas drive type underwater disconnecting device, mainly comprising three parts including a high pressure gas cylinder assembly, a high pressure electromagnetic valve assembly and a mechanical body assembly, wherein the three parts are connected through a stainless steel high pressure steel pipe and a high pressure pipe joint. A three-way ball valve is installed between the high pressure gas cylinder assembly and the high pressure electromagnetic valve assembly, and a one-way valve is installed between the high pressure electromagnetic valve assembly and the mechanical body assembly. The high pressure gas cylinder assembly is used for storing high pressure gas, the high pressure electromagnetic valve assembly is used for controlling the on-off of the high pressure gas in a pipeline, the mechanical body assembly is used for separating machinery and cables of a manipulator and underwater operation equipment, the three-way ball valve is used for changing gas circuits, and the one-way valve is used for preventing sea water from flowing into the gas cylinder after the manipulator is disconnected. When the underwater operation equipment normally works, the gas drive type underwater disconnecting device can provide accurate installation positioning for hand and shoulder joints of the manipulator and can be reliably connected with the underwater operation equipment. When the manipulator is in a dangerous condition, reliable separation of the manipulator and the underwater operation equipment can be realized so that the underwater operation equipment can be separated from the dangerous condition.