The utility model discloses a connecting device for reinforcing bar. The connecting device for the reinforcing bar mainly composed of a main sleeve and a fastening piece. The connecting device for the reinforcing bar has the advantages of being high in connecting intensity and convenient to install and construct. The installation and use are not limited by the factors such as the solidification of grouting material, and connection of the reinforcing bar can be realized quickly; in addition, when error occurs in the reinforcing bar installation and connection or connected reinforcing bars need to be released, the disassembly operation is the inverse process of the installing operation, the disassembly is convenient, and connecting pieces of the reinforcing bar after being disassembled can be reused, so that the material cost is facilitated to be saved, and the economical efficiency is good; in general, the connecting device for the reinforcing bar provides new connecting equipment and a new connecting technology for reinforcing bar connecting in a prefabricated unit, and the technical problem that simple and efficient connecting equipment is lack between reinforcing bars which cannot rotate in the fabricated unit in the prior art is solved properly.