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The high performance of alloys is dependent on microstructure. And, alloying elements have significant influence on microstructure. In order to study the effect of Si and Mn elements on the microstructure and mechanical properties, different content of alloying elements, Si and Mn, are added into the matrix Al-4.5Cu alloy. The compounded alloys (CA) were prepared by vacuum suction casting. The microstructure of CA is investigated by a scanning electron microscope (SEM). And, the mechanical properties are tested by a universal testing machine and a microhardness tester. Analysis is conducted by comparing experimental results of CA with different content of Si and Mn. It was found that the irregular lamellar structure of the CA appeared with the increase of Si and Mn content. The solid solution was coexisted with the irregular lamellar laminated structure when both Si and Mn contents are 3 wt.%. The tensile strength of CA is the highest when the content of both Si and Mn is 1 wt%. Its ultimate tensile stress reaches 205.87 MPa, the elongation reaches 34.97% and the microhardness reaches 74.6 HV. When both Si and Mn contents are 2 wt.%, the tensile strength of CA is the weakest. Its ultimate tensile stress reaches 146.65 MPa, the elongation reaches 24.15% and the microhardness reaches 60.2 HV. The elongation of the CA decreases with an increase in Si and Mn contents. [ABSTRACT FROM AUTHOR]