The influences of heating temperature and holding time on the microstructures were investigated during the semi-solid remelting process of rare earth Al-4.5Cu alloy. The evolution mechanism of crystal organization was discussed. Experiments show that the heating temperature and holding time are very important to the grain size and uniformity. It is the most suitable parameters, as heating temperature is 630°C and holding time is 20 minutes, to remelting process. During the remelting process, grain mergering and Ostwald growing up is the main mechanism of change on microstructures.