Based on finite rotation hypothesis, a rigid-flexible rotor dynamic model is developed. Comparing with classical finite element model, this model introduces three rigid degrees of freedom for hinge rotations coupled with blade elastic deformations and thus has potential advantages over the small rotation beam model. Generalized aerodynamic forces are tightly coupled with structural rigid rotations and elastic deformations. Structural loads are computed using three load calculation methods (force integration method, reaction force method, and curvature method) while equations of motions are solved on each step. The loads are examined by analysis results of BO105 model blade and flight test data of SA349/2 Gazelle helicopter. All load methods can handle the structural load calculation without aerodynamic forces applied. Force summation method loses some power at sections near the blade root especially when transient aerodynamic forces are taken into account. Results from curvature method and reaction force method are nearly the same at the nodes of finite element method. Accuracy of reaction force method depends on the response solutions and only shows efficient to predict loads at the nodes. Since curvature method simplify considers the bending and torsion deflections, it requires higher order shape functions to satisfy the continuity of second derivatives. To speed up convergence and decrease accumulated errors, extrapolation technique is introduced to implement numerical integration algorithm.