The bentonite waterproof blanket is installed in the underground waterproof (anti-seepage) project, which has the characteristics of long-term, self sealing, simple construction, environmental protection and high cost performance. Under the action of additives, bentonite particles form a uniform colloidal system with a permeability coefficient of 10-9cm / s, which fills the whole space. Under the restriction of artificial external force, the expansion of waterproof blanket changes from disorder to order, and the continuous water absorption expansion results in the waterproof blanket becoming dense and waterproof. Under certain high pressure, some bentonite particles can directly enter the small cracks of surrounding soil and concrete structure and expand when meeting water, which further ensures the waterproof and impermeability of underground engineering.