Foundation pit drainage device and drainage method

The invention provides a foundation pit drainage device and drainage method, and belongs to the technical field of foundation pit drainage, the foundation pit drainage device comprises a shell, a first interception piece, a second interception piece, a collecting cavity and a water pump unit, the shell is arranged at an opening of a water collecting well, and a top plate is arranged at the top of the shell; the first interception piece is arranged on the periphery of the top of the shell to intercept large-particle impurities; the second interception piece is arranged in the shell to intercept small-particle impurities; the collection cavity is arranged outside the shell, is communicated with the shell and is used for collecting the small-particle impurities intercepted by the second interception piece; the water pump unit is arranged outside the foundation pit and provided with a plurality of water pumps, each water pump is provided with a first water pumping pipe and a second water pumping pipe, the water s