The effects of dual aging process on microstructure and mechanical properties of as-cast Al-Si-Mg-Cu alloy were investigated by scanning electron microscopy， transmission electron microscopy and tensile test at room temperature. The dual aging process used in this study was low temperature pre-aging and high temperature final aging. The results showed that more precipitation nucleation sites were formed in the low temperature pre-aging stage of the alloys. After high temperature final aging， more θ" phases and some β" phases were precipitated in the alloys. When the pre-aging was 155 °C/8 h， the size of θ" phase gradually increased with the increase of final aging temperatures， while the morphology of the β" phase did not change significantly. The tensile strength of the alloys increased first and then decreased with the increase of the final aging temperatures. The elongation of the alloys decreased significantly with the increase of the final aging temperature， and 165 °C was the better final aging temperature of the alloy. When the dual aging process was 155 °C/x h+165 °C/2 h， the number of θ" phase and β" phase in the alloy gradually increased with the increase of pre-aging time. When the dual aging process was 155 °C/8 h+165 °C/x h， the size of θ" phase increased gradually with the increase of the final aging time. The number and size of β" phase in the alloy did not change significantly before the final aging time was 8 h. Continuing to extende the final aging time， the β" phase also began to grow. The dual precipitated phase strengthening of θ" phase and β" phase can be realized by optimizing the dual aging process. The tensile strength of the alloy can reach 380 MPa after 155 °C/8 h+165 °C/2 h dual aging， while the elongation of the alloy was increased to 3.4 % after 155 °C/8 h+ 165 °C/8 h dual aging.