The effects of different Cd contents on the microstructure and mechanical properties of Al-Cu alloy were studied through mechanical properties testing as well as SEM，EDX and TEM. The results show that the alloys with different Cd content have the similar aging response law in artificial aging process at 175 °C. Cd element can promote the precipitation of strengthening phase θ' of Al-Cu alloys. The time for peak aging of 0.19% Cd alloy and 0.36% Cd alloy was shortened and the peak hardness value was obtained upgrade. In the peak aging state, when the Cd element mass-fraction increased from 0.10% to 0.19%, the alloy yield strength increased from 384.2 MPa to 422.8 MPa, and the elongation decreased from 8.5% to 7.1%, but the yield strength did not change and the elongation decreased to 5.86% when the mass-fraction of Cd was 0.36%. TEM shows that the number of precipitated phases in the 0.19% Cd alloy was large and the size was small, so that the precipitation strengthening effect of the alloy was more obvious; the length of precipitated phases in the 0.36wt.% Cd alloy became slightly shorter, and the increase of the number was not obvious. At the same time, there was Cd-rich intercrystalline residual phase on the fracture surface of the alloy containing 0.19wt.% and 0.36wt.% Cd, which was harmful for improving the properties of Al-Cu alloy.