Cu-Ni-Nb alloy was fabricated by vacuum arc melting.The effects of Nb content on microstructure,melting point and thermal conductivity of Cu-Ni-Nb alloy were investigated.The results show that the Cu-Ni-Nb alloy is composed of Cu0.81 Ni0.19 matrix and the second phase of NbNi3.When the mass ratio of Ni/Nb is（6¹0）∶1,the second phase morphology in the Cu-Ni-Nb alloy exhibits all lamellar structure.When the mass ratio of Ni/Nb is（2⁴）∶1,the second phase morphology in Cu-Ni-Nb alloy presents the mixed structure of lamellar and particle structure.With the increase of Nb content,the solid solubility of nickel atoms in Cu-Ni-Nb alloy is decreased,so the melting point of the alloy is decreased,while the thermal conductivity is increased.The second phase in the Cu-20 Ni-5 Nb is fine lamellar and particle structure,which are distributed uniformly in the matrix.The second phase volume fraction reaches 19.2%,and the melting point of Cu-20 Ni-5 Nb alloy is 1 134.92℃ with its thermal conductivity up to 45.25 W/（m·K）,which can meet the requirements of manufacture and application of cast copper cooling water jacket.