The present invention discloses a liquid cooling system and a control method thereof. The liquid cooling system includes at least two second-level liquid circulation loops and a cooling control apparatus. One second-level liquid circulation loop is provided with a circulating pump configured to control a liquid flow and a sensing apparatus configured to acquire liquid sample data. The control method includes: acquiring liquid sample data by using sensing apparatuses of a liquid cooling system; implementing sharing of the liquid sample data of the sensing apparatuses by using a cooling control apparatus, performing analytical processing on the liquid sample data, and calculating a circulation regulation value of circulating pumps; and sending the circulation regulation value to the circulating pumps by using the cooling control apparatus, so that the circulating pumps run according to the circulation regulation value. In this way, all second-level liquid circulation loops run in a same running state, and when a liquid condition in one second-level liquid circulation loop changes, the circulating pumps on all the second-level liquid circulation loops can be adjusted simultaneously, so as to achieve system balance.