On the basis of different casting conditions such as normal gravity casting and high pressure die casting, the structure refining effect of die casting on the hypoeutectic Al-11Si-1.8Cu alloy is investigated by structure analysis. The research results indicate that compared with normal gravity casting, die casting can obviously refine the primary a-Al and eutectic Si phase of Al-11Si-1.8Cu alloy, and the morphology of primary a-Al changed from dendrite shape to spherical shape. Furthermore, under the condition of high pressure die casting, with the casting pressure increasing, the spherical morphology and size of primary a-Al are more round and small respectively, and the precipitaion of eutectic Si phase is suppressed simultaneously.