The utility model discloses a prestressing force system for final joint, final joint is including joint no. 1 and joint no. 2, it seals cyclic annular waterstop to be equipped with the round on the faying face of joint no. 1 and joint no. 2, the inner wall evenly sets up a plurality of adapting unit about in the of one along connecting, connect corresponding adapting unit who sets up the same quantity of inner wall about in the of two, every adapting unit who connects on one goes up the connecting pieces group of adapting unit constitution that corresponds with joint no. 2, connect an at leastprestressed steel beam between every connecting piece group. Utilizing this prestressing force system, realizing providing the waterstop through prestressed steel beam and last the compression, guarantee in the final joint installation and installation back waterstop is in the state of compressed all the time, prevent that water from getting into final joint inside, the waterstop atress is even simultaneously, prevents that final joint from sinking to strike when outside seawater pressure increases with continuouslying when putting to cause waterstop structure to destroy, the simple structureof this prestressing force system sets up conveniently, and is respond well.