Locked temperature is standard to evaluate railway stress and safety of railway. Strain electrical measuring method is used to monitor fluctuation of the locked temperature

and wireless sensor networks（ WSNs）is employed for data acquisition and transmission on-line monitoring test is carried out on 1500 meters-long continuous welded rail section for a month. During the test

the range of locked temperature fluctuation is calculated and compared. The fluctuation is large at the starting point near turnout area which is about ± 10 ℃ at the transition section it is small

which is about ± 5 ℃ and no more than ± 3 ℃ at the ballast section

respectively.The experiment result shows that the strain electrical measuring method meets the requirement for long-term and on-line safety monitoring for continuous welded rail.