In deriving the diffusion equation, diffusion tensor and dispersion relation in respect of the inhomogeneity in plasma, the Misquich-Balescu's theory on turbulence in uniform plasma can be generalized to the case of non-uniform plasma. It is indicated that the method given by Pelletier et al. in considering the plasma turbulence as a Markov process is now inadequate to describe the turbulence in non-uniform Plasma.