Abstract: Self action effects of intense laser beams interacting nonlinearly with preformed parabolic plasma channels have been investigated theoretically. Particularly the phenomena of self focusing, self channeling and self phase modulation of the laser beam arising as a consequence of the optical nonlinearity of the plasma channel have been investigated. Due to nonuniform irradiance over the laser beam, the ponderomotive force becomes active that alters the spatial density profile of the channel. As the index of refraction of the plasma depends on electron concentration, there is a resultant modification of the index of refraction of the channel in the presence of laser beam. This modification in the optical response of the plasma channel in turn alters the propagation dynamics of the beam envelope. Following Virial theory, a semi analytical solution of the wave equation for beam envelope has been obtained. Emphases are put on investigation of beam with and axial phase of the laser beam.