Abstract: It is one of the main causes of GFRP composite windturbine blades failure that the blade shimmy leads to the formation and growth of interlayer sliding cracks.The stress intensity factor K is an important parameter for the interlayer fracture toughness.It is also one of the important indicators for the safety assessment of surface cracks.On the basis of experiments, a new method for deriving K values from the displacement of the GFRP composite blade surface was proposed in this paper.The correctness of the theory was verified by experiments.It is proved by the comparison between experiment and simulation that it is feasible to study the interlaminar fracture toughness response through the surface displacement of the GFRP composite blades shimmy.This study provides a new idea and method for the strength prediction of GFRP composite windturbine blades.