Based on continuum mechanics, we have developed a model for semi quantitative estimating effects of phase continuity on flow strength of two phase rocks including partially melted or crystallized rocks. Calculations of the bulk flow strength of composite rocks as functions of the volume fraction, geometrical shape and continuity of the constitutive phases involve in numerically solving two non linear equations and thus are easy to be performed. The model has been justified by a good agreement between the predicted and measured results on diabase (64% clinopyroxene and 36% plagioclase) in the range of experimental temperatures and strain rates. It is believed that the present model could provide an approximate estimate for the rheological evolution of magmatic rocks during their life cycle of melting crystallization deformation. Based on continuum mechanics, we have developed a model for semi quantitative estimating effects of phase continuity on flow strength of two phase rocks including partially melted or crystallized rocks. Calculations of the bulk flow strength of composite rocks as functions of the volume fraction, geometrical shape and continuity of the constitutive phases involve in numerically solving two non linear equations and thus are easy to be performed. The model has been justified by a good agreement between the predicted and measured results on diabase (64% clinopyroxene and 36% plagioclase) in the range of experimental temperatures and strain rates. It is believed that the present model could provide an approximate estimate for the rheological evolution of magmatic rocks during their life cycle of melting crystallization deformation.