The structure design of gun according to the flow velocity and flow energy loss of the fluid in water cutting gun jet channel. Take the gun body plus filter method to solve when the water knife nozzle is small that easy jams. Adopt replaceable type jet tube solve appear jams when cannot promptly eliminate malfunction. Use adjustable grip handle solve the different length require in different surgery. Adopt casing tube wall approach to solving the negative pressure attract residual tissues and cells is not easy cleared.