A new cast copper alloy with excellent comprehensive mechanical properties of σ b≥550 MPa ,σ 0.2≥280 MPa,δ 5≥18% and a excellent corrosion resistance to seawater used for seawater pumper and valves was developed. In the seawater with a velocity of 7 m/s, the errosion rate of the alloy is 0.042 mm/a while in the sand-contained seawater with a velocity of 3.5 m/s, the errosion rate is only 0.144 mm/s. The difference of corrosion potentials between the developed alloy and （10/90） Cu-Ni alloy used for widely the seawater pump and valves is less than 100mV with a galvanic corrosion rate of 0.009 2 mm/a, which can effectively restrain galvanic corrosion of seawater pump and raise the service life of the pump and valves. Compared with other conventional copper for seawater pump and valves, the alloy subjeted to higher pressure possesses higher tensile strength and yield-strength ratio so that it can be widely used for the fields, such as deep-sea engineering.