The reflection spectrum from the Fiber Bragg Grating (FBG) sensors embedded in the composite was disturbed because of the thermal residual stress. In this study, two types of the FBG sensors, uncoated and UV-cured resin coated FBG sensors, were embedded in the triangle area of the T-stiffened composite panels. The strains during the curing process were measured by these two kinds of FBG sensors. Through the comparison of the results, it was found that the effect of thermal residual stress on the reflection spectrum could be attenuated when the FBG sensor was coated with UV-cured resin. Furthermore, the strain responses during the low-velocity impact test were observed by both two FBG sensors. The maximum-strain measured by the coated FBG sensors was more accurately than that measured by the uncoated one.