Human factors are the main causes for tunnel accidents and existing human error analysis models have flaws in quantification calculation and risk control. This paper presents the improved SReason analysis and control model, so as to reduce accidents during shield tunnel construction. Keeping in mind the characteristics of shield tunnel projects, the model improves the existing SReason model in two aspects: Firstly, the control difficulty weights of human errors are taken as the measures to find out the optimal control path of the accidents; Secondly, it cuts off the accident chains by preventing human errors in the optimal control path, while managing the end result by supplying feedback constantly through the feedback loop. By means of the said model, the paper analyzed the damage and failure of segment sealing material, disclosed human errors of staff at different levels in the optimal control path, and proposed corresponding control countermeasures. The comparison and contrast between the SReason analysis and control model and conventional methods shows that the improved SReason analysis and control model not only takes the factors of the organizations and the individuals into consideration, but also takes the economic efficiency and the safeness of the risk control into consideration. 