[Purposes] This study aims to research the flexural performance of near-surface-mounted (NSM) carbon fiber reinforced polymer (CFRP) strengthened beams with added non-prestressed sections. [Methods] A numerical model of the strengthened beam was established using the ABAQUS finite element software based on the test data. The bond-slip relationship between the CFRP plate and concrete as well as between concrete and steel bars was simulated by nonlinear spring elements. The numerical model was used to investigate the influence of different prestress levels of the CFRP plate, the bond length of the CFRP plate, and the length of the non-prestressed section at the end on the flexural performance of the strengthened beam. [Findings] The numerical simulation results were compared with the test results. Compared with the non-prestressed CFRP plate strengthened beam, the fully prestressed CFRP plate strengthened beam exhibits significantly improved flexural performance. With the increase in the bond length and the length of the non-prestressed section at the end, the flexural bearing capacity of the strengthened beam increases first and then decreases. The flexural performance of the strengthened beam is the best in the case of using a CFRP plate with the initial prestress of 900 MPa, the bond length of 2 300 mm, and the length of the non-prestressed section at the end to be 300 mm. [Conclusions] The comparison results show that the numerical model can accurately predict the ultimate load, crack development process, and failure mode of the strengthened beam.