The invention discloses a return-flow seawater direct-current cooling system, comprising a heat exchanger, and a water-taking pump communicated with an cooling water inlet of the heat exchanger, wherein a reflux pump which returns cooling water at the cooling water outlet to the cooling water inlet is arranged between the cooling water outlet and the cooling water inlet of the heat exchanger in acommunicated manner; the flow rate sum of the reflux pump and the water taking pump is a fixed value; the cooling water outlet is provided with a flow rate adjustment device which is used for adjusting the flow rate of the water taking pump and the reflux pump according to the water temperature of the cooling water outlet, when the temperature of the cooling water outlet is low, the flow rate adjustment device increases the flow rate of the reflux pump and decreases the flow rate of the water taking pump so that the seawater at the cooling water outlet enters the heat exchanger again and circulates for exchanging heat and the seawater at the cooling water outlet finally reaches the needed temperature. The system has simple structure and low equipment investment cost; and the energy consumption of the system can be effectively reduced by recycling the cooling water.