This paper presents a study on the reliability analysis and online measuring of sensors in Structural Health Monitoring (SHM) systems. As sensors are critical components in SHM, their reliability and accuracy are vital for the precise and effective operation of the monitoring system. By utilizing a strain testing platform and online measurement methods, this study analyzes the reliability and effectiveness of in-service sensors by comparing measurements on similar positions and applies the indoor experiment to an actual bridge structure. The results demonstrate that the proposed method can achieve precise reliability analysis and online measuring, ensuring the effectiveness and smooth operation of the SHM system and further enhancing the fundamental safety level of bridges while providing convenience to bridge management.