Abstract: The momentum integral technique for predicting the boundary layer growth in three dimensional flow along the rotor chordwise has been developed.The aerodynamic characteristics of the forward skewed rotor and the straight rotor have been simulated,analyzed and compared at the off design regimes.The boundary layer thickness of the forward skewed rotor decreases in the top of blade due to reduction of the secondary flow loss.This fact conforms with experimental investigation.The conclusion that the forward skewed rotor has a higher efficiency and wider off design performance is validated once more.