Abstract: The classical geometrical fitting, which only use the interpolation and approximation to fit the given data points, cannot satisfy the streamline constraint. An improved NURBS curve fitting method for turbine blade and airfoil profile was proposed by considering constraint of streamline field. The constraints include the accuracy and continuity at the data points, which are used as the geometrical constraints, and the maximal lift as the physical constraint. The NURBS-formatted analytical expression of the lift, deduced from the aerodynamics, is solved to obtain the fitting model by using the optimization method. The case study and CFD simulation demonstrate that the new NURBS curve fitting method with the streamline constraint can improve the working performance compared with the geometrical fitting method.