We propose the design of nanotapered bus-waveguide to enhance the waveguide-to-cavity coupling. By enlarging the mode-field diameters of the high-index integrated waveguide with a nanotaper, the coupling strength can be doubled comparing to the conventional coupling of a uniform bus-waveguide. In addition, by utilizing the discretization of transfer matrix, the coupling between tapered bus-waveguide shows a good agreement with the finite-difference time-domain method. This nanotaper design provides the flexibility for coupling optimization, especially the ideality in the overcoupled regime.