We propose a distributed fiber sensor based on optical frequency domain reflectometry (OFDR) for strain measurement on a wind turbine blade. Due to the varying cross sections along the heterotypic blade, the strain distribution is nonlinearly demonstrated in experiment as estimated and predicted in numerical analysis. Negative strains (compression) and positive strains (tension) are detected in the 177-198 cm and 224-245 cm regions of the fiber, respectively. Moreover, responsivities of -0.77571 με/g and 0.59953 με/g at 195 cm and 228 cm are proved to be inversely proportional to the local cross sections, with a linearity quantified by R2 values of 0.99987 and 0.9999. This technique provides an effective method to characterize strain in heterotypic structure, showing potential in defect positioning by stress concentration as well.