An underwater gas bubble may have a unidirectional movement, after impacting with a ratchet, which consists of asymmetric teeth with gradient inclination. In this work, the corresponding movements were first experimentally investigated. Small bubbles are easily pinned on a ratchet surface. In contrast, large bubbles have directional transportation from large to small inclination areas. Since the detected motions could not be interpreted using existing propulsive mechanisms, a new propulsive mechanism was then developed. Based on the new mechanism, two approaches to manipulate bubbles have been investigated experimentally.