The invention discloses a hydraulic auto-oscillation control system for a fire water monitor, which comprises a hydraulic cylinder, a watercourse base plate, a hydraulic change valve and a mechanical feedback device, wherein the hydraulic cylinder comprises a cylinder body, a piston, a piston rod, a cylinder body end cover and the like; the hydraulic change valve comprises a valve plug, a valve body, a positioning end cover, an end cover spacer and the like; and the mechanical feedback device comprises a bumping head, a bumping block, an adjusting handle, a drive bracket and the like. When the valve plug is positioned at a left position of the valve body, water enters a left cavity of the cylinder body, and the piston rod moves rightwards, when the piston rod moves to a certain position, the bumping block positioned on the left side presses the bumping head to plug a water outlet, and then the pressure of the left cavity of the cylinder body increases to push the valve plug to move rightwards; and when the valve plug moves to a right position of the valve body, water enters a right cavity of the cylinder body, and the piston rod moves leftwards. Under the action of the water power, the control system can drive the piston rod to move back and forth so as to drive a fire water monitor head to jet at a certain angle and in a certain oscillating frequency, has a wide coverage and is in particular suitable for a large space and the places where firefighters are unapproachable.