The invention discloses a lower exhaust steam pipe drainage system of a low-layout water feed pump turbine and a drainage method, and solves the problem about drainage of a lower exhaust steam pipe ofa low-layout water feed pump turbine. When the liquid level of a drained water collection box (10) is lower, a pump-front drainage shutoff valve (19) and a vacuum breakdown shutoff valve (14) are closed, a valve-front shutoff valve (7), a valve-back shutoff valve (8) and a vacuum pumping shutoff valve (12) are opened, and drained water of a waste steam exhaust pipe (2) automatically flows into the drained water collection box by altitude difference; when the liquid level of the drained water collection box (10) is higher, the valve-front shutoff valve, the valve-back shutoff valve and the vacuum pumping shutoff valve (12) are closed, the vacuum breakdown shutoff valve (14), the pump-front drainage shutoff valve (19), a first pump-back drainage shutoff valve and a second pump-back drainageshutoff valve are opened, the drained water in the drained water collection box is discharged into a condenser (4) by a drainage pump (17). Safe operation of the water feed pump turbine is guaranteed, and the generating capacity requirement of the unit is met.