DyadicGreen's function (DGF) technique is a very efficient means of dealing with the electromagnetic boundary-value problems. In this paper, the dyadic Green's function of ionospheric waveguide was constructed on the basis of quasi-parabolic electronic concentration distribution of the inhomogeneous ionosphere. As a practical application, two physical models with sources in ionosphere and at the earth's surface were discussed. The coefficients of dyadic Green's functions corresponding to the two models were derived by using the boundary conditions of DGF at the interfaces. The forms of dyadic Green's functions possesses a pretty good symmetry with regard to the source and observed points. Although the consideration was based on two special physical models, the final results can be generally used to the practical problems with slow variation relative permittivity with regard to the radial coordinate.