By using the Olympus GX71 microscope, the effects of Al-5Ti-B addition, holding time and holding temperature on the microstructure of Al-5Cu alloy have been studied, and the influencing rules have been got. The experimental results show that the refinement effect of Al-5Ti-B is very remarkable and the grain sizes of Al-5Cu become small. The optimal parameters are as follows. The refiner addition is 2%-3%, and the holding time is 15 minutes, and the holding temperature is 720°C-740°C. When the 2%-3% Al-5Ti-B refiner is added, the Al3Ti is fine needle shape and the precipitation phase Al2Cu is round flake shape or reticular shape. Simultaneously, the dendrites have minimum spacing, and the microstructure becomes fine and uniform.