The invention discloses a method of designing and optimizing Al-Si-Cu-Mg system phase change heat storage alloy materials. The method includes confirming a thermodynamics data bank and thermodynamics calculation software of a Al-Si-Cu-Mg quaternary system, selecting one component of alloy of the Al-Si-Cu-Mg quaternary system, calculating heat content when the selected component of the Al-Si-Cu-Mg quaternary system is in 25-2500 DEG C, finding a 400 DEG C heat content and a 800 DEG C heat content from a data file, using the 800 DEG C heat content to minus the 400 DEG C heat content, obtaining enthalpy change of the selected component of the Al-Si-Cu-Mg quaternary system, comparing sizes of the enthalpy change of alloy of different components of the Al-Si-Cu-Mg quaternary system from 400 DEG C to 800 DEG C, selecting components of alloy with big enthalpy change, and conducting steps, such as alloy smelting and calorimeter experimental verification. The method is simple and convenient, easy to implement, and capable of saving time, improving efficiency and reducing test and materials cost, and does not need a large amount of raw materials and test.