In this paper the fatigue performance of strengthened steel plate girders with CFRP strips was investigated using numerical models. The cracked plate girders were strengthened by different reinforcement configurations at high damage level of web plate. The research confirmed that the strengthening by CFRP strips leads to a significant increase of the fatigue life and reduction of the crack propagation, especially the strengthening for both flange and web. Moreover, the study proposed V-Shape strengthening system by CFRP strips around the crack in the web plate. Consequently, the results demonstrated that U-shape strengthening system with prestressed CFRP has the best efficiency for fatigue strengthening. On the other hand, the fatigue analysis based on stress life method was performed by using S-N curve to predict the actual total fatigue life for the steel plate girder without initial damage. Therefore, the results showed that the fatigue damage of plate girders starts to appear at maximum loading (0.5P_y). Furthermore, the load capacity and the age at which the strengthening should start were studied as parameters. Finally, the results concluded that an early repair for plate girders is more efficient in improving the fatigue performance, especially when the bridge is subjected to heavy loads.