Abstract: A new refinement agent of Al-Mg-Cu-（La） alloys was prepared by fluoride salt method. The effects of fluoride salt reaction time on the microstructure evolution of Al-Mg-Cu-（La） alloys were studied by experimental test. The results show that the reaction time between aluminum melt and fluoride salt does not change the phase structure of the alloys. After adding La element, the characteristic peaks of Al₂Cu and Al Mg phase still exist. At the same time, the diffraction peaks of the Al₃Mg La are detected. The grain sizes of the second phase of Al Mg and Al₃Mg La formed in Al-Mg-Cu-La alloy are smaller than those of Al-Mg-Cu alloy, and the addition of La element can exert the effect of metamorphism and refinement on Al Mg mesophase. A higher proportion of Mg is formed in the alloy by increasing the reaction time. La can accelerate the chemical reaction process between fluorine salt and aluminum melt, play an obvious catalytic effect, and make Al reach a more adequate reaction degree.