Abstract: The DSC analysis was usually used to determine the phase transition temperature of alloys. For the Al-Si-Cu-Mg alloys, the differential heating（DSC） absorption peak area was related to the number of θ phases（Al₂Cu）, supplemented by SEM+EDS detecting the results of DSC analysis. The results show that the DSC absorption peak area decreases from 0.6 J/g in the as-cast state to 0.1 J/g after solid solution at 500 ℃ for 4 h. Moreover, with the increase of solid dissolution time, the absorption peak area does not change significantly, which is consistent with the detection results of θ phase（Al₂Cu） dissolution under scanning electron microscopy. All indicate that Al₂Cu basically dissolves into the matrix after being kept at 500 ℃ for 4h, achieving a good solid solution effect. It proves that DSC can be used to detect the degree of solid solution of the phase, and it has the feasibility of being furtherly applied to the formulation of heat treatment processes.