Remote sensing satellite structures are susceptible to thermal strain during in-orbit service due to extreme temperature changes in space and microgravity environment, which seriously affects the detection accuracy. However, the existing methods are difficult to achieve thermal strain monitoring in orbit. To solve this problem, a thermal strain fiber grating monitoring method with temperature decoupling function is proposed. The thermal strain of the structure is calculated and analyzed by numerical simulation, and the change of temperature and strain fields under overall and local thermal loading are obtained. A thermal strain fiber optic monitoring test system is designed and constructed, thermal loading fiber optic measurement test on satellite antenna structure specimens is conducted, the accuracy of structural thermal strain fiber optic monitoring is tested and analyzed, and the effectiveness of the method is verified. Research results show that in the temperature variation range of -120-120 ℃, the monitoring accuracy of temperature and thermal strain by fiber Bragg grating sensor and temperature decoupling method are 1.02% and 2.45%, respectively. The reconstruction errors of the structural temperature and strain fields are 3.24% and 6.61% under the action of local thermal loading from 30 ℃ to 100 ℃, respectively. The method has the prospect of application in satellite structure in-orbit health monitoring.