Concrete-filled steel tubular (CFST) T-joints are advanced structural components used in bridges, offshore platforms, and high-rise buildings. This study conducted a parametric analysis on eight square-section CFST T-joints under seismic loading using Abaqus software. The numerical models were validated against experimental data from the literature, showing good agreement (within 6.2% for ultimate load). The hysteresis behavior was evaluated based on ultimate load, deflection, stiffness, ductility (μ=2.8–4.2), and energy dissipation (ζhyst=8.5–12.3%). Key parameters investigated included core concrete strength (30–60 MPa), brace wall thickness (4.2–6 mm), and brace section dimension (60–100 mm). Results indicate that increasing the brace dimension by 66% raises ultimate capacity by 67% and reduces maximum displacement by 39–55%. In contrast, a 43% increase in brace wall thickness yields only a 7.5% capacity gain. Doubling concrete strength increases capacity by 11%. The novel contribution of this study is the systematic comparison of these three design parameters, revealing that brace dimension is the most effective variable for enhancing seismic performance. Thus, the most effective measures for improving load-bearing capacity are, in order: increasing the brace dimension increasing concrete strength increasing brace wall thickness.