A new technique for measuring micro angular displacement is presented. Based on a symmetrical metal-cladding waveguide, ultrahigh-order modes in the guiding layer(air gap) can be excited through prism coupling to serve as sensitive probes. When a micro angular displacement of the objective occurs, the thickness of the air gap as well as the effective refractive index of the mode will be tuned. As a result, the intensity of the reflected beam will change remarkably with a magnitude proportional to the angular shift. It is shown through numerical calculation that the sensitivity is directly affected by the effective refractive index of the probe mode. A cantilever-like structure is employed in the experiment to generate controllable angular displacement, the mean sensitivity has been measured and found to be in well accordance with the results predicted by theory (relative error ～39%). It is theoretically and experimentally shown that, for components with a centimeter-sized rotational radius, an angular resolution of the order of 10-9 rad can be successfully achieved by this technique.