The invention discloses a waterproof structure and a waterproof method for a tunnel. The waterproof method for the tunnel comprises the following steps: applying guard posts on two sides of a to-be-excavated tunnel, carrying out slot broaching and excavating to apply a longitudinal cross beam on an existing ground, and pouring a top plate in the longitudinal cross beam; paving a waterproof plate on the top plate, stretching two sides of the waterproof plate below the outer side of the longitudinal cross beam, paving a protecting layer on the waterproof plate, and paving a pavement on the protecting layer to recover surface traffic; carrying out cover and excavation top-down construction, excavating rock soil among the guard posts in the same row to reserve a mounting space, paving a drainage pipe clinging to a surrounding rock, and communicating the drainage pipe to a drainage ditch; applying a breast board among the guard posts in the same row, connecting the upper part of the breastboard to the top plate and connecting the lower part of the breast board to a bottom plate, applying waterproof layers on the surfaces of the guard posts and the breast board, and applying a side wallon the inner sides of the waterproof layer and the top plate. The waterproof structure and the waterproof method for the tunnel can shorten the surface construction period. The waterproof structure is effective in waterproofness by taking measures of the drainage pipe, the waterproof layers and the like in a discontinuous waterproof paving form.