A lumped kinetic model has been developed for the methanol to olefins (MTO) reaction over phosphorus modified HZSM-5 catalyst. In consideration of mixed feed cracking, a higher reaction temperature than the conventional MTO reaction was chosen. The reaction temperature considered is in range of 500 to 680 °C. The experimental data for the kinetic model were obtained in an isothermal fixed bed reactor over a wide range of operating temperatures and space time of 0.160 to 0.801 g-cat.h/mole of methanol feed. A reaction mechanism comprising seven lumps was utilized to analyze the kinetic behavior of this catalyst. Based on the mathematical kinetic model for the fixed bed reactor, the kinetic parameters were determined by numerical optimization using a hybrid of genetic algorithm and active set gradient method. The developed kinetic model reasonably predicts the experimental data obtained for the reaction conditions considered. It has been found that increasing space time is favorable to light olefins yield, while a maximum water free basis olefin yield of about 82weight % was obtained at a temperature of 630 °C for a space time of 0.801 g-cat.h/mole of methanol feed.