Abstract: Vertical water temperature stratification will occur after large reservoir is built and impounded. It is of great significance to study the variation law of vertical stratified water temperature in reservoir area for the establishment of scientific water ecological regulation scheme. In this paper, the principle and application range of distributed optical fiber temperature measurement system are studied. The application of vertical stratified water temperature monitoring in front of Xiluodu dam and Xiangjiaba dam was studied by system integration, data processing technology and data comparison method. The application results showed that the distributed optical fiber temperature measurement system can meet the monitoring requirements in terms of stability, data continuity and accuracy, and can provide reliable data reference for water ecological regulation in the reservoir area. It provides a new way for the application of vertical on-line monitoring of water temperature in the reservoir area in the future.