This paper studies the flexural fatigue performance of damaged steel beams strengthened by carbon fiber reinforced plastic-optical fiber bragg grating (CFRP-OFBG) plates. By analyzing the test beam's failure mechanism under cyclic loading and the strain data monitored by the CFRP-OFBG panel in real-time, a life prediction model based on cumulative fatigue damage is proposed. The test results show that CFRP-OFBG plate reinforcement effectively reduces the fatigue crack growth rate of damaged steel beams and increases the fatigue life of damaged steel beams by 22.46%. The analysis and test results show that the minimum error between the calculated value of the life prediction model and the test value is -24.13%, and the maximum error is -5.61%. This study provides some suggestions for improving the service life of existing fatigue-damaged steel beams and establishing a simple fatigue life evaluation model.