To provide a waterproof method and a waterproof structure for performing the waterproof of the wall surface of a building by simple means.

By a simple method for, in the case of closing a clearance S to be formed between a hole 1 formed on a wall surface H of a building T and a cylindrical body 2 projected outward from the hole 1, adhering an L-cross-sectioned waterproof adhesive tape 3 to the wall surface H of the building T and the side surface of the cylindrical body 2 at the same time to adhere the L-cross-sectioned waterproof adhesive tape 3, it is possible to close the clearance S to be formed between the hole 1 formed on the wall surface H of the building T and the cylindrical body 2 projected outward from the hole 1.