When composite structures are exposed to the space environments such as low earth orbit,they are known to undergo considerable temperature change.Therefore,for the successful completion of their missions,it is important for the structures to maintain the consistent dimensional stability in such a thermal cycling condition.The coefficient of thermal expansion (CTE) of the structures is suitable to express the dimensional stability and it is needed to be monitored throughout the mission.In the experiment,two fiber Bragg grating (FBG) sensors have been adopted for the simultaneous measurement of thermal strain and temperature to get the CTE change.LEO conditions with high vacuum,ultraviolet and thermal cycling environments were simulated in a thermal vacuum chamber.The change of the transverse CTE in a composite laminate exposed to the space environment was measured for intervals of aging cycles in real time.As a whole,there was no abrupt change of the CTE after 1000 aging cycles.After aging,however,the CTE decreased a little all over the test temperature range.From the experimental results,it was shown that FBG sensors can be successfully embedded into the composite structures to monitor strain and temperature simultaneously，which can check the health status of spacecrafts under low earth orbit over long-term mission time.