Currently most of the aerodynamic shape design of wind turbine blades is still based on the blade element-momentum (BEM) theory with 2D airfoil data from wind tunnel experiments or CFD predictions. 3D stall delay phenomenon happens, resulting in great difference of airfoil loading from the 2D data. A general model for 3D stall delay, related with all the possible parameters, are proposed by use of the Πtheorem Based on NREL Phase VI experimental data, comparisons and analysis of two 3D stall delay models, Chaviaropoulos & Hansen and Du & Selig models are made. The model parameters in Chaviaropoulos & Hansen models are systematically tested. A correction for improving this model is put forward and compared with the experimental data.