Mode characteristics of a free-standing microdisk with an output waveguide are investigated by three-dimensional finite difference time-domain technique. For a microdisk with a diameter of 5μm, thickness about 0.35μm, and refractive index of 3.4, connected to a 0.4-μm-wide output waveguide, the coupled mode has a Q factor in the order of 10⁴, and the in-plane emission efficiency of 0.4, which is defined as the ratio of the radiation energy in the output waveguide to the total radiation energy. The effects of the output waveguide width and the microdisk thickness on the Q factor of the coupled mode and the in-plane emission efficiency are also discussed.