The invention relates to a hydropower station ground plant tail water outlet structure which comprises a tail water pipe connected with a hydraulic turbine set. The tail end of the tail water pipe is provided with a tail water pressure pond which is a pond with the opened top and the closed bottom and side faces, the tail water pressure pond is communicated with the tail water pipe, and the top of the tail water pressure pond is provided with an overflow opening capable of draining tail water in the tail water pressure pond downstream; and the overflow face elevation of the overflow opening is lower than the downstream maximum flood control water level and is higher than the downstream design tail water level. The hydropower station ground plant tail water outlet structure is feasible in technology, simple in structure, reliable in running, suitable for hydropower stations with large tail water level variation amplitude and without needs for sufficiently using the lowest tail water level.