Abstract: The preparation of high−performance magnesium hydroxide from salt lake bischofite is a current research hotspot. Improving the one−pass conversion rate of magnesium ions is of great significance for reducing energy consumption and enhancing the market competitiveness of magnesium hydroxide. Using bischofite, the main by−product of the potassium extraction process from salt lakes, as the raw material, magnesium hydroxide was prepared via the ammonia forward precipitation method. The effects of reaction temperature, stirring speed, ammonia concentration, and reaction time on the one−pass conversion rate of magnesium ions were investigated. Through single−factor experiments, real−time monitoring of pH and conductivity during the reaction, and characterization techniques, the influencing mechanisms of reaction temperature, ammonia−to−magnesium molar ratio, stirring speed, and reaction time on the magnesium ion conversion rate were analyzed. The results indicate that among the factors affecting the magnesium ion conversion rate, the optimal critical temperature is 50 ℃, the stirring speed is 700 r/min, and the ammonia concentration is 7.2 mol/L. Prolonging the reaction time does not significantly improve the magnesium ion conversion rate. Under the optimal conditions, the one−pass conversion rate of magnesium ions reaches 92.25%. Reaction temperature, ammonia−to−magnesium molar ratio, and stirring speed exhibit significant interactive effects on the magnesium ion conversion rate. This study is expected to provide a reference for the efficient utilization of magnesium resources in salt lakes and the industrial production of magnesium hydroxide.