Using the axial-vector coupling and the electromagnetic form factors of the D and D* mesons in 2+1 flavor Lattice QCD, we compute the D*Dpi, DDrho and D*D*rho coupling constants, which play an important role in describing the charm hadron interactions in terms of meson-exchange models. We also extract the charge radii of D and D* mesons and determine the contributions of the light and charm quarks separately.