We designed a CFRP-FBG sensor with a “sandwich” structure consisting of carbon fiber reinforced polymer (CFRP) encapsulation layers and a fiber Bragg grating (FBG) for strain monitoring of wind turbine blades. This design aims to protect the FBG sensor while maximizing the strain transfer from the CFRP to the FBG sensor. Strain and temperature experiments showed that the linear correlation coefficient of the experimental CFRP-FBG sensor’s central wavelength change-strain evolution curve was above 0.9999, and the repeatability error of the strain sensitivity coefficient was 0.1665%, demonstrating high accuracy and repeatability. Meanwhile, CFRP-FBG was tested in full-size turbine blades in operation, during which time they were subjected to millions of dynamic strain cycles and various loading environments. The results of 11 months of monitoring showed that the CFRP-FBG provides real-time, reliable, and highly accurate strain measurements and can meet the needs of long-term blade strain monitoring.