We investigate theoretically the tuning properties of the resonant mode of the waveguide-grating structures (WGS). This intends to understand how tuning mechanisms of the waveguide resonance mode depend on the structural and the geometric parameters of the WGS device, which can be used as guidance for the design of biosensors and other optoelectronic devices. The device parameters studied here include the angle of incidence, the thickness and refractive index of the waveguide, the period of the grating, and the refractive indices of the substrate and the medium on top of the grating. In particular, the control of the tuning rate and the adjustment of the tuning range by optimizing the combination of the relevant parameters provide a practical route for the design of biosensor and optical switch.