The model effective index for Ge20Sb15Se65 rib waveguides are calculated using the finite difference method. The group velocity dispersion properties of the quasi-TM single polarization of waveguides are systematically studied around the optical fiber communication wavelength (1550 nm), and their relationship with the key structural parameters of the waveguide is also studied. Extensive simulation results show that the larger material dispersion can be reduced through the design of sub-micron waveguide structure. The rib width and height are controlled in the range of 500～900 nm and 400～1000 nm, respectively, zero dispersion or anomalous dispersion can be obtained by increasing the etched depth. In addition, the impact of rib width on dispersion is less obvious than that of rib height. The investigation results provide the basis of the size design and dispersion management for the chalcogenide optical waveguide applied to nonlinear all-optical devices. The results have some reference value to the design of chalcogenide glass optical waveguide devices used in all-optical signal processing.