Abstract: The micromechanics Bridging Model constitutive theory of composite materials was incorporated with finite element software ABAQUS through a user subroutine UGENS to analyze the progressive failure process and ultimate strength of a composite wind turbine blade, which has a complicated three-dimensional geometry. Under the input of the constituent fiber and matrix properties, fiber volume fraction, and skin and rib lamination parameters such as lamination angle, thickness and number of laminas used, the software was able to estimate the overall load-carrying capacity of the wind turbine blade and to locate the position where the blade ultimate failure took place. Based on this, the composite wind blade structure can be effectively evaluated, and an optimization in structural design can be achieved easily. The thus developed method has been applied to the design and analysis of a 20kW composite wind turbine blade with an advanced structure, and favorable results with improved strength and stiffness and reduced weight have been obtained. This method is also well applicable to the ultimate failure analysis and strength design of other complicated composite structures.