The microstructure and mechanical properties of the Al_0.7CoCrFeNiCu high-entropy alloy (HEA) were studied in both as-cast state and annealed state, and the results showed that the alloy was composed of FCC1, FCC2, and BCC phases. Cu-rich and Fe-Cr-rich precipitates were present within the BCC phase, while small amounts of needle-like precipitates were observed in both the FCC1 and the FCC2 phases. After annealing at 700°C, the matrix phase composition of the alloy did not change significantly, but the volume fraction and size of the needle-like precipitates increased with the holding time. The hardness and yield strength first increased and then decreased with the extension of the holding time, reaching peak values at 48 h of holding time of 364 HV and 667 MPa, respectively. During annealing at 900°C, the volume fraction of needle-like phases first increased and then decreased with prolonged holding time, while the precipitates underwent significant coarsening. The hardness and yield strength reached peak values at 1 h of holding time of 311 HV and 493 MPa, respectively. During the subsequent holding process, as the needle-like phase significantly coarsened, the mechanical properties of the alloy steadily declined, which led to the overall mechanical properties after annealing at 700°C being superior to those after annealing at 900°C.