Steel welded circular hollow section (CHS) joints are widely adopted, and the corrosion induced degradation threaten the safety and reduce the residual life of them after long-term service. To study the performance of grout-filled GFRP tube repairing corroded circular hollow section (CHS) T-joints, a total of six specimens, including uncorroded, corroded unrepaired and grout-filled GFRP tube repaired CHS T-joints were tested under brace axial compressive loading. The experimental results show that the corroded joints with around 10% chord weight loss ratio may lead to about 20% reduction of the ultimate strength. The grout-filled GFRP tube repairing is effective to prevent the ovalization of the chord, by which the joint failure mode changed from chord plasticization into chord punching shear. The ultimate strength and initial stiffness of the repaired chord corroded joints are enhanced by 100% and 50%, respectively, which are higher than those of the corresponding uncorroded ones. Based on the verified finite element models, further parametric analyses indicate that the diameter ratio of the brace to the chord, the thickness of the GFRP tube and the section hollow ratio of the repaired chord are critical parameters that determine the repairing effect. By contrast, the length of the repairing cover and the strength of the grouting layer are found to be less influential. By optimizing the configuration of the grout-filled GFRP tube repairing, the ultimate strength of the corroded joint with 28% chord weight loss ratio can be enhanced by more than 1.5 times to its corresponding uncorroded one. Finally, suggestions are proposed for the repairing of joints with different corrosion ratios, to achieve a 20% ultimate strength enhancement than uncorroded joints after repairing. The current study can provide a reference for both repairing and improving performance of corroded steel tubular joints after long-term service.