大坝变形是大坝观测主要物理量之一，也是评估大坝工作性态，监控其安全运行的重要指标。变形监控指标一般可分为正常值、警戒值和极限值。变形极限值是重要而又难以拟定的，值得深入研究。本文重点探讨推求重力坝运行期变形极限监控指标值的基本原理、表达公式和计算方法，并结合实例予以应用。 Dam deformation is one of the major physical quantities observed by the dam. It is also an important index for evaluating the dam behavior and monitoring its safe operation. Deformation monitoring indicators can be divided into normal, alert and limit values. Deformation limit value is important and difficult to draw, it is worth further study. This article focuses on the basic principle, expression formula and calculation method of deducing the monitoring index value of deformation limit in the operation period of gravity dam, and applies it with examples.