A high-expansion building waterproof reinforcing material made of polyisocyanate and polyether polyol. The product can expand to several tens of times in volume within a few minutes after the water is solidified. The solidified body formed after solidification is insoluble in water, high in strength and stable, and can be quickly plugged for long-term water intrusion areas with high water pressure. The product itself can also absorb the same amount of water molecules in the air and have the same chemical reaction. It can also play a good role in filling and sealing the relatively dry gap and achieve effective and perfect waterproof effect.