This application provides a liquid cooling heat dissipation system, which includes a control unit, a heat source box, and a heat dissipation unit. A temperature sensing unit is installed in the heat source box, and the temperature sensing unit and the control unit are connected for signal transmission. The heat dissipation unit includes an inlet and an outlet. Coolant flows into the heat dissipation unit through the inlet and flows out of the heat dissipation unit through the outlet. A flow regulating valve is disposed on a pipe at the inlet, and the flow regulating valve and the control unit are connected for signal transmission. The control unit obtains temperature information by using the temperature sensing unit, and determines lowest temperature T1 and highest temperature T2 based on the temperature information. The control unit is configured to control an opening degree of the flow regulating valve.