In order to conduct in-depth research on the stress redistribution state of the lining GFRP protective composite pipe wall at the corrosion defect pit in its original pipeline and its repair effect. A mathematical model of corrosion defects in pipelines was established using the equilibrium differential equation within elastic-plastic mechanics. A pipeline model containing a single corrosion defect was established using the finite element method, and the stress state at the corrosion defect pit before and after repair was compared and analyzed by changing the depth ratio of the corrosion defect pit. The analysis results indicate that the depth ratio of corrosion defect pits has a significant impact on the stress distribution of pipelines, so attention should be paid to the influence of corrosion pit depth when conducting pipeline safety assessments. During the process of increasing the depth ratio of corrosion defect pits from 0.1 to 0.8 in stages, the circumferential stress, radial stress, and Mises stress at the corrosion defect site on the pipe wall show an increasing trend. The circumferential stress at the corrosion defect pit before repair is similar to the Mises stress, while the radial stress is smaller than the previous two and the circumferential stress is the largest among the three. Before and after repair, the control stress at the corrosion defect of the pipeline is generally the circumferential stress, and the failure of the pipeline can be judged based on the circumferential stress. After repair, the inner lining of the GFRP protective composite pipe wall experienced stress redistributions at the original corrosion defect pit, and both the circumferential stress and Mises stress decreased, indicating a significant repair effect.