A new form of power matrix is proposed to correct the unreasonable points in traditional statistical multi-input multi-output (MIMO) channel model which mishandles different power variations in different polarization direction. Based on the analysis of modeling theory of different diversities, a composite calculation method of power matrix and covariance matrix is proposed to build a general-purpose statistical channel model which exactly represents statistical characteristics under the effects of space-diversity and polarization-diversity, and thus can be applied to arbitrary diversity MIMO systems.