The invention relates to a multifunctional boiler water treatment agent, which is characterized by comprising the following components: 40-58 wt% of catalyzed potassium sulfite, 5-10 wt% of isoascorbic acid, 2-8 wt% of diethylenetriamine, 10-15 wt% of trisodium phosphate, 16-20 wt% of sodium carbonate and 5-8 wt% of sodium hydroxide. The multifunctional boiler water treatment agent of the invention can remove dissolved oxygen from boiler water rapidly, and solves the corrosion problem of boilers, pipelines and heat exchangers. The multifunctional boiler water treatment agent provided in the invention can also lessen the boiler water hardness, reduce and prevent scale formation, and employment of the treatment agent can control the boiler water oxygen content within the scope of national standards. The multifunctional boiler water treatment agent in the invention also has residual hard scale removing and scale prevention effects.