The method of seismic strengthening the RC frame T-shaped joints with FRP was designed. Its significant effect of seismic reinforcement was verified through cyclic loading tests. The joints models were established using finite element analysis software ANSYS. The whole process of monotonic loading at the beam end were simulated numerically in order to study in depth of the mechanism of FRP reinforcement. Experimental results and numerical simulation analysis showed that: fibers wrapped in the core area of the joints could improve the strength of concrete, and bear part shear of the joints; bending fibers at the beam-column end played to take parts of the moment and reduce the stress of longitudinal bars in the corresponding parts, thus improving indirectly the bearing capacity and ductility of the members strengthened using FRP increased; the stiffness of the joints strengthened with FRP increased when identical loading.