The low temperature early strength coagulant for magnesia cement is prepared with water 35-45 wt%, concentration 30 % NaOH solution 20-30 wt%, beta-chloropropionic acid 12-25 wt%, and monoethanolamine 10-20 wt%. It is prepared through mixing the first mentioned three kinds of material in reactor via stirring, reaction at 50-60 deg.c for 60-90 min, adding monoethanolamine slowly, heating to 85-95 deg.c, stirring while maintaining the temperature for 90-120 min, cooling to room temperature and canning. The present invention is added into magnesia cement slurry and has the features of shortening the coagulation time at low temperature, raising the early strength of the product, shortening demolding time, raising production efficiency and lowering production cost.