Abstract: It is aimed at monitoring the steam temperature change in the tubing-casing annulus and in the steam injection pipe of horizontal section during cyclic steam stimulation, so as to provide the data support for the field steam operation. The distributed temperature sensing (DTS) technique was adopted, which monitors the temperatures in the tubing-casing casing and the horizontal section based on the technological string structure of binding the optical fiber to the outside of insulated tubing and running the Y pipe into the tubing of horizontal section. Owing to the application of DTS, the temperature data in the full hole in four stages (pre-steam injection, steam injection, soaking and blowout) were obtained successfully. The analysis on the measured shows that the highest temperature in the horizontal section during steam injection is up to 368.22 ℃. The returning of steam is monitored in real time and controlled by taking the corresponding measures according to the change trend of annulus temperature so as to ensure the safety of steam injection. The field tests indicate that the heat insulation performance of the insulated tubing can be evaluated by monitoring the tubing-casing annulus temperature in the process of steam injection, and monitoring the temperature change in the horizontal section in the stages of soaking and blowout can provide the accurate testing data support for the subsequent steam stimulation effect analysis and numerical reservoir simulation.