Abstract: The effects of different factors, such as saturation temperature and cooling rate, on the metastable zone width (MSZW) of the NH₄Cl-MgCl₂-H₂O system were investigated using a laser method. The experimental results show that the MSZW narrows with decreasing cooling rate and increasing saturation temperature and stirring rate, which affects the nucleation and crystallization of the system, slowing down the nucleation rate of the target crystal, ammonium carnallite. Additionally, the nucleation kinetic parameters of MgCl₂·NH₄Cl·6H₂O were calculated using the Self-consistent Nývlt-like equation and the classical three-dimensional nucleation theory model, providing relevant references for optimizing the production process of ammonium carnallite. The study of MSZW and related kinetics is beneficial for improving the particle size and yield of ammonium carnallite, and is significant for optimizing the crystallization process and the preliminary design of crystallizers.