By using four cross-type RC frame joint models with a 1:2 scale ratio, with one comparative test piece and three reinforced test pieces, a reinforcement can be achieved of the test piece under the secondary force by CFRP net reinforced high performance composite mortar. By adopting a combined method of both experimental research and numerical simulation, an exploration has been made into the effect of strengthening frame joints based on this method, followed by a research conducted on the influence of the change of axial compression ratio on the strengthening effect, including the failure form, bearing capacity and ductility, hysteretic curve, skeleton curve and energy dissipation capacity of the strengthened specimens. The results show that CFRP net has reinforced high-performance composite mortar is an effective reinforcement method for frame joints in that within a certain range of axial compression ratio, the energy dissipation capacity and ultimate bearing capacity of reinforced specimens increase with the increase of axial compression ratio, while their ultimate displacement and ductility performance decrease with the increase of axial compression ratio. The numerical simulation results of shear capacity of reinforced joints are in good agreement with the experimental results, which verifies the reliability of the model.