In order to analyze the influence of different dimensions on aerodynamic performance prediction of wind turbine airfoil, the flow fields surrounding 2-D airfoil of DU93-W-210 and 3-D straight blade were simulated by solving the N-S equations. Experimental results were compared to predict aerodynamic performances. The results revealed that if the flow did not separate, the aerodynamic performance and streamline between the 2-D airfoil and 3-D straight blade were similar, and the 3-D straight blade could be simplified into 2-D airfoil. If it separated, the flow field of 3-D straight blade had significant 3-D flow effects, the predicted aerodynamic performance was closer to experimental value than 2-D airfoil, but the 3-D straight blade could not be simplified into 2-D airfoil. The best span wise length of 3-D straight blade was 2~4 times of the chord.