The invention discloses a depth-frequency-conversion riverside make-up water system of a closed-cycle cooling unit. The system comprises a make-up water pump, pipeline boosting pumps, a cooling tower,users of the make-up water system and the like. The pumping head of the make-up water pump is reduced by increasing the pipeline boosting pumps, the flow adjustment range of the make-up water pump isincreased due to the fact that a part of users supplied with water by the riverside make-up water pump originally are supplied with circulating water instead, the situation that the riverside make-upwater amount is larger than water demand of the cooling unit and the tower tank of a cooling tower overflows is avoided, accordingly, the rotation speed of the make-up water pump is controlled through a frequency conversion control device of the make-up water pump according to the make-up water amount required by the cooling unit, the flow of the make-up water pump is adjusted, the make-up watersystem runs in the optimal state, and the best energy-saving and water-saving effect is achieved. With the adoption of the depth-frequency-conversion riverside make-up water system of the closed-cyclecooling unit, power consumption of the riverside make-up water system can be reduced, the riverside water intake amount can be reduced, overflow of the tower tank of the cooling tower is reduced, andthe overall economic efficiency of a thermal power plant is enhanced favorably.