Magnesium metal production from bischofite is a process of high energy consumption. It is necessary to explore the process of lowest energy consumption. In this work, with anhydrous magnesium chloride and magnesium oxide as intermediate products, electrolysis and thermal reduction as key methods, a comprehensive process network from bischofite to magnesium metal was constructed, which involved 24 species, 20 chemical processes and 25 process routes. Furthermore, one minimum energy consumption model was proposed to evaluate the thermal effect of multi–chemical process, or multi–process routes. Using the standard enthalpy of formation and temperature-depended isobaric molar heat capacity, the energy consumption and heat removal of all 25 process routes were calculated. The results showed that the optimum path based on thermal reduction method was converting bischofite to magnesium hydroxide by lime method, calcining to obtain magnesium oxide, and further reducing to magnesium metal by aluminum. The energy consumption was 360.15 kJ/mol, and the heat released was –315.46 kJ/mol. Compared with this, the better path of electrolysis was producing magnesium hydroxide by lime method, calcining to get magnesium oxide and further producing magnesium metal by electrolyze in molten electrolyte. The energy consumption of the process was 738.54 kJ/mol, and the heat released was –135.42 kJ/mol. Because of the high energy consumption of anhydrous magnesium chloride preparation, it was not in the optimal path.