The effect of cooling rate on the solidification microstructure of Cu-Ni alloy is investigated here. The Cu-Ni alloy was prepared in a main frequency furnace with three different molds made of silica sand, graphite, and low carbon steel in the foundry. The simulation software of diathermanous-flowing-stress coupling PROCAST is used to simulate the Cu-Ni alloy solidification process about temperature field with the three molds. The microstructures of the alloys have been studied through the optical microscopy (OM), the scanning electron microscopy (SEM), together with the energy dispersive spectroscopy (EDS).The results show that the grain average size and the primary and secondary dendrite arm space were obviously reduced with the increase of cooling rate. The dendrite and interdendrite element segregation also decreases with increasing cooling rate.