a coring bit back reaming function, relating to the petroleum gas rock core drilling equipment manufacturing field, comprises a steel body and a carcass which is arranged at the front end of the steel body; an inner cutting face and an inner conical surface are arranged on the inner circle of the carcass; a front cutting face is arranged at the front end of the carcass; a front conical surface, an outer gage surface and a back taper surface are arranged on the outer circle of the carcass. The utility model solves the problems of difficult unfreezing when the collapse is serious or the well wall has a large shrinkage; the utility model employs the back reaming mode, designs a back-reaming coring bit with back taper teeth capable of reaming upwards, can perform long-distance back reaming when the coring operation is blocked, cut off the blocking rocks and remove drill-sticking accidents.