The strength analysis of an existing 5-meter composite wind turbine blade using Tsai-Wu and Puck failure criteria is presented. Finite element analysis is performed on the blade under static flap wise loading. ANSYS APDL scripting language is used to implement Puck failure criteria and degradation rules for the progressive failure analysis of the blade. Evaluation and visualization of Tsai-Wu inverse reserve factors and Puck failure exposures in the blade is done with the help of the Ansys ACP/Post module. The results of this study indicate that the blade is not able resist extreme load case and needs to be redesigned. Root and trailing edge of the blade have the highest risk of failure initiation. Linear analysis using Tsai-Wu and Puck failure criteria is compared with the nonlinear analysis using progressive Puck failure criteria. It is concluded that progressive analysis is necessary for a more realistic simulation of blade failure mechanisms. Results of the analysis will be used to calibrate structural test set-up of the blade.