Abstract: A method of strain measurement and deformation reconstruction based on modal method is investigated in view of the needs of real-time deformation monitoring of antenna array structure in the field of phased array radar. This method uses fiber Bragg grating sensors to measure the surface strain of the panel and realizes the conversion from strain to displacement through modal theory, and the shape of the reflection surface is reconstructed. Taking a phased array radar experimental platform as the research object, its modal displacement matrix and modal strain matrix are extracted by finite element software, and the strain-displacement conversion matrix is calculated. Through experimental measurement, the panel strain values under various working conditions are extracted, and the shape of the reflection surface is reconstructed by modal method. The reconstruction results are compared and analyzed with the actual displacement values. The results show that the modal method can relatively accurately reconstruct the deformation of the reflection surface.