随着地铁、公路等交通隧道的不断发展，隧道往往穿越江河湖泊等水体，大直径泥水平衡盾构广泛应用于水下隧道施工。大直径盾构施工风险高、控制难度大，加上水下施工不确定因素多，风险因素具有不断动态变化的特点，使得施工过程中存在较大的风险。风险评估越来越多地应用于水下隧道施工安全管理中。本文介绍了大直径泥水盾构的几个特点，并对这几个特点引起风险增大的机理进行了分析，针对风险评估常用的几种方法中存在的不足，提出了一种适用于类似工程的指数法，给出了该方法的评估流程及基本计算模型，并将该方法初步应用于某水下隧道施工风险评估。该方法能够适应风险因素的变化，并且不拘泥于真实概率，通过进一步的细化和完善，能够更好地适用于水下隧道施工安全风险评估。

With the unceasing development of the traffic tunnels in subway and highway engineering, sometimes the tunnels pass through rivers or lakes, so slurry shield method with large diameter is often used in the underwater tunnel construction. The underwater tunnel with large diameter has the characteristics of high risk, difficult to control, more uncertain risk factors, which will cause greater risk in construction process. Risk assessment is more and more applied in underwater tunnel construction safe management. The characteristics of using slurry shield with large diameter in underwater tunnel were introduced in this paper, and the mechanism that how the characteristics arouse the increase of risk was analyzed. According to the disadvantages of previous risk assessment methods, an improved index method was put forward, and the assessment process and main calculate model of this method were given. This method has been used in an underwater tunnel in Nanjing subway engineering, the application results show that this method can adapt the dynamic change of risk factors and it can be better applied in underwater tunnel construction safety risk assessment.