Six kinds of Cu-Ni alloys with different sulfur contents were investigated at room temperature for tensile properties. The effects of tensile rate and sulfur content on the yield strength, tensile strength, elongation, and reduction of area of the alloys were studied. The changes of metallographic structure with sulfur content were studied by scanning electron microscope (SEM), energy disperse spectroscopy (EDS) and metallographic structure analysis. The distribution and deformation of sulfur precipitate and the influence law for the plasticity of Cu-Ni alloy were analyzed. The origin and occurrence of alloy fracture process and the influence mechanism of sulfur content on plasticity were analyzed, providing a theoretical basis for subsequent cold deformation process.