The injected 2s-3d two-photon resonant parametric oscillation in lithium vapor has been studied theoretically and experimentally. It's output, compared with general pamametric oscillation, has better monochromaticity and appears as a "sharper" conical radiation. Furthermore, the injected parametric oscillation is tunnable as we change the frequency of the seed beam on the red side of the 2s-2p transition of lithium atom.