The invention belonging to the field of the cooling technology for the converter valve, discloses a flexible direct-current converter valve cooling system for an offshore platform. When the ambient temperature is low, the system uses seawater as cooling water for cooling and cooling water in a water storage branch is kept to be at a low temperature; when the temperature of cooling water in a maincirculation loop can not meet a requirement of the water inlet temperature of a converter valve, the main circulation loop and water storage branch are communicated and the stored water with the low temperature in the water storage branch is used for reducing the temperature of the cooling water, so that the water inlet temperature requirement of the converter valve is met and the converter valveworks safely and stably. Therefore, a problem that the seawater can not be used reasonably for cooling a converter valve in the prior art is solved. According to the system, fresh water is used as a cooling medium and the whole system is a totally enclosed circuit; the seawater is used for cooling the cooling water, so that the cooling capability of the system is enhanced; and no complicated seawater treatment link is needed. Moreover, the system has advantages of simple structure, low cost and good cooling ability.