The calculation of the beam waist diameter and it′s position of an intracavity Raman shift laser is discussed. We use optical transformation matrix and figure out the general pump field parameters in the Raman gain medium. And then, according to Ibison′s "matched mode" theory, the Stokes field parameters in the Raman active medium are calculated. By using the optical transformation matrix again, the Raman shifted beam (emitted from the optical system) parameters can be calculated. The results provide a new base for Raman shifted laser design.