The invention discloses an underwater low-disturbance separation device and belongs to the technical field of mechanical structures. The underwater low-disturbance separation device is applied to a vertical floating warhead of a long-range self-propelled naval mine. Due to the low-disturbance separation function of the underwater low-disturbance separation device, the initial launching disturbance of an engine can be reduced, finally the quality of a floating trajectory is improved, and trajectory distribution is reduced. In the service period, the vertical floating warhead is moored underwater in a two-point mode through the separation device and a mooring system installed at the tail portion of the vertical floating warhead so as to be concealed for waiting to make an attack; when an attack instruction is received, the engine is started, and the internal pressure of the engine is rapidly increased through generated fuel gas; when the internal pressure reaches a certain value, a limiting plug of the separation device is pushed to cut off a shear pin and move downwards, and limiting on a steel ball is relieved; and when the working pressure of the engine is larger than the environment pressure, an inner shell of the separation device moves and is separated from an engine connecting flange, a connecting rod is driven to disengage from the vertical floating warhead, and the warhead is separated from the mooring system and starts to vertically float to attack a target. Sealing, underwater two-point mooring, underwater ignition liberation, underwater corrosion resistance, parasitism resistance and the like of the underwater floating warhead can be realized through the underwater low-disturbance separation device.