Monitoring displacement of a wind turbine blade is much more difficult, especially under extreme load and fatigue load conditions. The conventional displacement measurement techniques, such as linear variable differential transducers, micrometer gauge and others, are the so-called contact measurement. The contact measurement is a high-precision measurement for small deformations at discrete points on the object. However, they suffer from several disadvantages as the measurement range is very limited and the measurement system has a complex layout when the number of measured points increases. As a result, it is very difficult to measure the displacement of a wind turbine blade using the contact measurement in the full-scale range due to the complexity of layout and expensive cost.