The analysis of failure properties of wind turbine blades is the important foundation for the stability and reliability analysis of the whole machine. By combining the finite element simulation with the full scale static load test, the deflection properties of the 100 kW medium sized experimental blade developed by IET, Chines Academy of Sciences under different load conditions are obtained. The study focuses on the failure properties of blades under large load conditions, and with the experimental data and finite element simulation results, the failure risk area and failure mechanism are analyzed. It is determined that the cause for fracture failure of the blade is the interlayer failure caused by the shear stress under heavy load and the consequential degradation of the resin material.