Connecting device for improving drawing effect of cast-in-place pile in anti-drawing test

The utility model relates to the technical field of cast-in-place pile pull-out test accessory devices, in particular to a connecting device for improving the pull-out effect of a cast-in-place pile in a pull-out test. A plurality of main reinforcements are reserved at the top of the cast-in-place pile; the connecting device comprises a plurality of first reinforcing steel bars, a middle tray and a plurality of connecting assemblies, the tops of the first reinforcing steel bars are used for the hydraulic jacking device, the connecting assemblies comprise second reinforcing steel bars and connecting pieces, and the connecting pieces comprise connecting lug plates, first threaded pipes and second threaded pipes, and the first threaded pipes and the second threaded pipes are arranged at the two ends of the connecting lug plates. The bottom ends of the multiple steel bars are inserted and screwed into the top ends of the multiple first threaded pipes correspondingly, and the tops of the multiple main bars are ins