<p>Due to the geometric complexity and spatial confinement of impeller flow channels, a five-axis roughing strategy that allows flexible tool orientation is typically adopted to ensure efficient material removal. However, most existing tool orientation planning methods fail to make full use of CAD model’s design information, resulting in collision-prone tool orientations in complex flow channels. To solve this problem, a feature-driven two-stage interpolation method is proposed for tool orientation planning in five-axis impeller roughing. In the proposed method, a rule-based feature algorithm is presented for constructing boundary feature-driven surfaces, which define the machinable region of the flow channel. Based on the constructed boundary feature-driven surfaces, machining-driven surfaces are generated to determine the boundaries of the tool paths. Subsequently, a two-stage interpolation strategy is proposed for smooth tool orientation planning. At the first stage, key tool orientations are extracted along the tool path boundaries and projected onto the boundary feature-driven surfaces so that the resulting orientations avoid collisions. These orientations are selected as data points for non-uniform rational cubic B-spline interpolation of tool orientation, which produces a continuous and collision-free sequence of tool orientation within each path boundary curve. In the second stage, a tool orientation smoothing method based on spherical quadrilateral interpolation is presented for each path segment, ensuring smooth and collision-free tool motion. Finally, simulations and experiments are conducted to validate the proposed method.</p>