To evaluate, calibrate equipment, and check the safety of THz devices etc, biotissue phantom is needed for these purposes. Although various researches about biotissue phantom using water have been done, such phantoms are not ideal. Because of the evaporation of water, the optical properties of a phantom change as the time goes by, since THz radiation is very sensitive to the water concentration of the sample. We chose graphite as the substitute of water, and therefore the water-free biotissue phantom was developed to mimic the similar optical properties as human tissues. In order to determine the concentration of each component precisely, quantitative analysis is needed. In this work, we used several mathematical models of the effective medium theory, including the Polder and van Santen model, the Landau, Lifshitz, Looyenga model, the model of complex refractive index, and the Bruggeman model, to study the influence of different graphite concentrations on the refractive index of the water-free biotissue phantom. Phantoms with different graphite concentrations were simulated and 3 phantoms with different graphite concentrations were produced to evaluate the reliability of each model. The fabricated phantoms were then compared with stomach tissues. The result also shows the promise that by using the proper mathematical model, correct concentration can be calculated for other tissue phantom.