The operation optimization tests of cold end system are conducted by double speed operation innovation of water circulation pump in two 1 036 MW steam turbine units of Huaneng Haimen power plant. According to the test data, the slight increasing curves of exhaust steam pressure and power are fitted, the correction formula of power is obtained, and the characteristics at variable operating conditions of condenser are calculated. Combined with the integrated coal and electrovalence comparison method, the operation mode for water circulation pump by double speed operation innovation is recommended. It is proved that the double speed operation of water circulation pump can reach the goal of energy saving and obtain the maximum economic benefits for the power plant.