To solve the problem of insufficient flexural bearing capacity of T-beam of T-beam bridge in service, a new combined reinforcement method combining enlarging section with external prestressing was proposed. The finite element method was used for simulation analysis. Compared with the traditional method, the composite reinforcement method has satisfactory safety reserve coefficient, and the transverse connection of bridges is strengthened. It solves the problem that the high-pressure area may be too large when the T-beam bridge is strengthened by external prestressing.