Abstract: Five-axis machining is widely used in fine machining. Sometimes to modify the machining velocity/acceleration in the interpolation period with single-spline fitting method can be demanding. With dual-spline fitting method the tool axis vector and the tool point coordinate in the tool position file can be separately calculated, so that the kinematics within processing can be effectively adapted without impairing the fitting accuracy. In this paper, a dual spline fitting method will be introduced to simulate the processing of S-shape workpiece with B-spline least squares curve fitting and S-curve speed planning carried out. It will be then compared with the common five-axis spline interpolation method to prove the feasibility and practicality of dual-spline method