This paper presents a new tool orientation optimization approach for multi-axis machining considering up to second order kinematical performance of the multi-axis machine. Different from the traditional optimization approach, tool orientations are optimized with the goal of improving the kinematical performance of the machining process, not only increasing the material removal from purely geometrical aspect. The procedure is to first determine a few key orientations on the part surface along the tool path according to the curvature variation. Key orientations are initially optimized to be able to achieve high material removal by comparing the tool swept curve and the actual part surface. Intermediate orientations between key orientations are interpolated smoothly using rigid body interpolation techniques on . The time-optimal trajectory planning problem with velocity and acceleration constraints of the multi-axis machine is then solved to adjust the initially determined tool orientations to better exploit the multi-axis machine’s motion capacity. Simulation and experiment validate the feasibility and effectiveness of the proposed approach.