The utility model provides a be used for inside drainage system in highway sag vertical curve bottom road surface includes surface course, basic unit and bed course from top to bottom, wherein in proper order the basic unit permeates water to set up between basic unit and the waterproof basic unit and passes through the seal including setting up permeate water basic unit and the waterproof basic unit of setting in the below in the top the basic unit outside sets up sump pit and transverse drainage pipeline, the rainwater, converges in the sump pit to pass through the seal on through surface course, the basic unit's seepage flow that permeates water, through the transverse drainage pipeline again with rainwater drainage to the structure of road surface outside. The utility model discloses a big particle diameter water permeability asphalt concrete basic unit of permeating water, the use of cooperation sump pit and transverse drainage pipeline can enough reduce rigid base's reflective cracking, and outside road surface and roadbed structure were in time got rid of to the moisture in the structure of road surface of stagnating in a large number again, it was bad to reduce between inside ponding problem in road surface and layer the damage by water, with the performance that greatly improve the road surface with prolong road life.