  In this paper we construct a self-consistent renormalization group procedure
for MHD turbulence in which small wavenumber modes are averaged out, and
effective mean magnetic field at large wavenumbers is obtained. In this scheme
the mean magnetic field scales as $k^{-1/3}$, while the energy spectrum scales
as $k^{-5/3}$ similar to that in fluid turbulence. We also deduce from the
formalism that the magnitude of cascade rate decreases as the strength of the
mean magnetic field is increased.
