With the development of highway traffic, many aging bridges urgently require rehabilitation. This study focuses on the parameter analysis and design of prestressed concrete box girder bridges strengthened with transverse steel connections (TSC). Using a specific TSC reinforcement project for a multi-girder bridge, a finite element (FE) parametric analysis was conducted to investigate the effectiveness of transverse reinforcement under different scenarios. The analysis explored various TSC configurations and optimized designs to determine the most effective reinforcement strategies. Key parameters, such as TSC geometry (i.e., H-shaped, K-shaped, and tri-shaped TSCs), material properties, connection configurations, and load conditions, were systematically varied to assess their impact on the bridge’s performance. The results showed that the tri-shaped TSC configuration significantly improved the load-bearing capacity and reduced deflection by 15% compared to other shapes, demonstrating the critical role of geometry in reinforcement effectiveness. These findings provide valuable insights into the behavior of TSC-reinforced bridges and highlight the critical factors influencing their effectiveness.