<p>Engineered cementitious composites (ECC), as a novel class of high-performance construction materials, are increasingly employed to enhance the mechanical behavior and seismic resilience of structural elements. To further explore the seismic performance of ECC-reinforced beam-column joints, this study develops a computational model to examine the influence of critical design parameters on the seismic response of such joints. Initially, a finite element model of an ECC-integrated beam-column joint (EBC) was established through numerical simulation. The validity and reliability of the numerical model were confirmed by comparing the simulation outcomes with experimental data. Subsequently, the effects of key design variables—including ECC length, strength, thickness, and concrete compressive strength—on the seismic performance of the joints were systematically analyzed. The results indicate that ECC length and thickness have a pronounced influence on seismic behavior. Extending the ECC length from 240 to 640 mm increases the yield displacement by 64.26% and the peak load by 28.65%. Similarly, increasing the ECC thickness from 10 to 50 mm enhances the peak load by 12.83%. However, elevating the ECC strength from 40 to 80 MPa results in only a marginal improvement in peak load capacity, while significantly enhancing the hysteresis performance. The influence of concrete strength on seismic performance is relatively minor. To support practical design applications, a quantitative predictive model (R² = 0.985) and a theoretical shear capacity model (prediction errors &lt; 15%) were formulated. These findings provide meaningful theoretical guidance for the design and optimization of EBC.</p>