The invention provides a method for coaxially connecting two FRP reinforcements by an FRP connecting pipe and an expansive cement, comprising the following steps of respectively perforating two reinforcements to be connected with coaxial holes, coaxially connecting and positioning the two reinforcements by an FRP extruding/pulling rod or a wire rope, sheathing a section of FRP connecting pipe at the joint of the reinforcements; carrying out coaxial positioning by a positioning ring at two ends of the connecting pipe; arranging a pouring opening or an air outlet on the positioning ring during horizontal pouring process and injecting expansive cement solution between the reinforcements and the connecting pipe by the pouring opening; needing not to arrange the pouring opening or the air outlet on the positioning ring during vertical pouring process, firstly installing and then sealing the lower positioning ring; putting the upper sealing ring in place after completing pouring the cement solution to beexpanded from the upper opening along the wall of the FRP connecting pipe, thus ensuring the coaxiality of the reinforcements and the sheathed pipes. The hardening time of the expansive cement is 6-12 hours generally. The FRP pipe can be prefabricated, the quality thereof is easy to be controlled, the cost of the expansive cement is low, the connection construction is simple and convenient, and the connecting part prepared by the expansive cement has light weight, high strength and corrosion resistance and can be used for structures with demagnetization requirements.