In order to improve the mechanical properties, a new Al-5Ti-1B-1RE master alloy refiner and Al-10Sr master alloy modifier were used to composite refine and modify the as-cast A356 aluminum alloy and a novel aluminum alloy composed of as-cast A356 aluminum alloy by adding Cu, Mn, Ti and other elements in a certain proportion. The morphology distribution of the second-phase particles and strengthening mechanism of the multi-component aluminum-silicon alloy were analyzed by means of OM, SEM, TEM and the electronic universal testing machine (CSS-44100).The results showed that the second-phase eutectic silicon phase in the A356 aluminum alloy transformed from coarse lamellar to typical fibrous phase after the composite refinement and modification, and precipitated uniformly at the grain boundary of the soft-tough phase α-Al matrix. The grain size of the α-Al phase decreased significantly. It was mainly Hall-Petch grain boundary fine grain strengthening mechanism. In addition to the second-phase particle eutectic silicon in the novel aluminum alloy, there were other second-phase particles which were more dispersed in the grain boundaries or intragranular. Various strengthening mechanisms worked together. When the second-phase particles were distributed on grain boundaries, it was mainly the Hall-Petch strengthening mechanism. When the second-phase particles were distributed in intragranular, it was mainly Orowan strengthening mechanism, which became an effective obstacle to dislocation movement and played a strengthening role.