This paper takes the solid Cu-9wt%P alloy as the research object, and studies the dissolution process of solid Cu-9wt%P in molten aluminum at 973 K. Through static dissolution and water quenching experiments, the solidification structure that retains the dissolution process information is obtained. ZEISS Axio Vert.A1 optical metallographic microscope and scanning electron microscope (Scaning electron microscope, SEM) were used to analyze the solidified structure. The study found that when the solid Cu-9wt%P alloy is dissolved in molten aluminum, with the extension of the dissolution time, single-phase Cu3P is easily formed on the side of the Cu-9wt%P alloy on the solid-liquid interface, and the front of the solid-liquid interface is enriched with particles and Layered AlP. The dissolution process of solid Cu-9wt%P alloy in aluminum melt is summarized, and the root cause of the slow dissolution rate is revealed.