To satisfy the increasing requirements of small size yet high-loading capacity in the modern industrial and aerospace technology, a novel worm drive consisting of a planar internal gear and a crown worm is demonstrated. The crown worm is generated by the planar internal gear surface. Theoretical calculation confirms that small induced principal curvatures, big sliding angles and large meshing area exist on the conjugate surfaces, indicating that the new worm drive is of smaller contact stress and better lubrication. A new machining method for crown worm is proposed based on the principle of virtual center distance. Performance test is carried out to confirm the practical use of this novel worm drive. The contact area is carefully evaluated by means of both the gear meshing theory and the performance test on the prototype. This study is expected to give rise to a new insight on the design of the future miniature device for aerospace applications as well as other fields.