The utility model relates to a cooling water system for a hot lean oil pump. The cooling water system comprises an oil pump, an oil inlet pipe, an oil outlet pipe, a cooling water inlet pipe and a cooling water outlet pipe, wherein the oil inlet pipe and the oil outlet pipe are arranged on the oil pump, the cooling water inlet pipe and the cooling water outlet pipe are arranged on the oil pump, a check valve is also arranged on the water inlet pipe, two sides of the check valve are respectively provided with diameter changing joints, and the check valve is arranged on the cooling water inlet pipe through the two diameter changing joints. In order to prevent wash oil from entering the cooling water system, the check valve is arranged at an inlet part of a cooling water pipeline, so when the cooling water pressure is smaller than 0.35MPa, medium wash oil in the lean oil pump cannot enter the water system, and the water pollution phenomenon is avoided. In order that the check valve can be matched with the cooling water pipeline of the hot lean oil pump, two sides of the check valve are provided with two kinds of diameter changing joints, and the check valve can be conveniently and fast arranged on the cooling water pipeline of the hot lean oil pump through the diameter changing joints.