Abstract: Optimal technique based on Response Surface Methodology (RSM) is employed in a multiobjective optimization design of a 1.5MW horizontal axis wind turbine (HAWT) blade with NPU-WA series airfoils for wind turbine application used along the span. The software of PROPID51 for the design and analysis of HAWT based on Blade Element Momentum (BEM) theory is used to predict the aerodynamic performance. The design variables are the blade shape parameters including chord and twist distributions along the span while relative thickness distributions are maintained. The objectives of the model are the maximums of Annual Energy Production (AEP) and power coefficient. A composite function called desirability function is built using the weighted sum of the individual objective function. The reduced quadratic polynomial without the secondordercross items are used as RS model to reduce the computational cost and the set of design points is selected to satisfy D optimality. The optimal design is performed on a 1.5 MW variablepitch and variablerpm wind turbine blade and the NPU-WA series airfoils developed in Northwestern Poly. Univ. for wind turbine application are used along the span. The calculated aerodynamic performance of airfoils is used as inputs in optimal design to analyze the effects of the weight factor of the individual objective function; experimental aerodynamic performance at free transition condition is used in design as well and the effects on aerodynamic performance of HAWT for clean and soiled surface conditions are analyzed.