In the light of phenomenon of local buckling of blade appeared under aerodynamic loads,the paper established the finite element shell model of large-scale composite wind turbine blade,and mainly studied the stability of blade structure under the effect of flow field. Based on fluid-solid coupling method,the paper calculated the distributed stress of blade surface by aid of CFD software . It introduced the calculation results into the finite element model of the blade structure, and carried out the buckling analysis of blade .Taking the blade of 1.5MW composite wind turbine for example, the results show that the compressive properties of composites are weaker than tensile properties of that, the leeward side of blade subjects to compressive load,the local buckling mainly appeared on the leeward side surface of blade. The trailing edge region from the development of leaf blade root is located in the geometric catastrophe zone.The structure design of trailing edge is weak so it is necessary to increase the thickness of layer.