The effects of MgCl2 and NaCl concentration, stirring speed, temperature and cooling rate on solubility and supersolubility of KCl were systematically investigated by using laser method in MgCl2-H2O system. Two models were presented to simulate and predict the solubility of KCl, and results between predicted and experimental ones were compared. The solubility and supuersolubility were increased with increasing temperature or decreasing MgCl2 concentration. The predicted results were well consistent with the experimental data. Crystallization metastable zone width (MSZW) was significantly narrowed with increasing NaCl concentration, while the stirring speed and cooling rate had less effect on MSZW.