High pressure treatment is one of the most important methods in sterilization technology without using high temperature. High pressure technology is used for improving the reological properties of food too. one of the important advantages of high pressure treatment of food is enzymes inactivation without loss of nutrients and taste. The problem of high pressure equipment installation is one of the limitation of this technology, thus many reresearching have been carried out to solve this problem; for example use of supercritical fluids, especially supercritical CO 2 that cause to decrease the needed pressure level in treatment. Process modeling and simulation is needed in order to provide additional data in this research. Therefore the objective of this thesis was to study different models for this technology. Three mathematical models, Weibul, Log- logistic and Gampertz model, were solved with a numerical method to produce the survival curve of microorganism. For validate the models, data were compared with experimental data. The Log- logistic model produced best fit to all survival curves and the Weibul model was good but not as well as the Log- logistic and Gampertz model was the poorest. We tried to fit the Log-logestic model to the pressure cycling experiments but the result indicated that there is no compatibility between experimental and models data.