Abstract: Fractured rocks and naturally fractured vuggy Carbonate reservoirs are classified as complex porous media, characterized by complex pore systems, the size of which can range from nanometers or micrometers of micropores to tens of centimeters for large fractures and solution vugs. Due to the poor approximation in single-continuum model and the inability to describe the complex geometry of the surface bounding the void spaces at the microscopic level, multiple-continuum approach has to be adopted for transport phenomena analysis for most practical problems. The concept of representative elementary volume for multiple-continuum model is quantified. Multiple-continuum approach can be adopted for the complex porous media only if a representative elementary volume of multiple-continuum model can be defined in the field-scale domain. Porosity and permeability are selected as relevant state variables for the demonstration. The relationship between the representative elementary volume of multiple-continuum model and that of single-continuum model is investigated. A method to estibilish multiple-continuum model for the complex porous media is also presented.