Concrete-filled steel tubular (CFST) columns are recognized as a cost-effective alternative to other composite columns, with their most significant advantage being the reduced steel consumption compared to conventional steel-profile columns. In construction practices in countries such as Japan, the use of internal and external stiffening plates is widely common in the connections of such structures. Employing these plates can serve as an effective and efficient method for strengthening CFST column connections. In this research, to validate the finite element model, an experimental specimen of this type of connection, previously studied by Xiong et al. in 2017, was selected, and the numerical and experimental results were compared and verified. Subsequently, using the validated model, 19 numerical models across six different groups—with variables including opening size, concrete compressive strength, application of FRP sheets, columns with variable core concrete sections, and corrugated plates—were analyzed. The results demonstrated that the use of CFRP sheets significantly enhances the ultimate load-bearing capacity and also reduces plastic stress and strain. This led to a decrease in buckling in the connecting plates and transferred stress concentrations to the adjacent columns. Under identical conditions, the specimens strengthened with CFRP sheets exhibited higher load-bearing capacity and a lower rate of strength degradation after reaching peak load. Specifically, the specimen equipped with a CFRP sheet and without any opening, with a load-bearing capacity of 651.1 kN, showed approximately 37.4% higher capacity compared to its counterpart without any reinforcing sheet. Furthermore, this specimen demonstrated 40.4% and 25.6% higher load-bearing capacity along with lower strength degradation compared to specimens with opening diameters of 15 mm and 5 mm, respectively. The combination of corrugated plates with CFRP sheets markedly improved the performance of the models; for instance, Specimen 18 (featuring a corrugated plate with a 2 cm flange size and a CFRP sheet) recorded an average of 48% higher load-bearing capacity than the other specimens.