The uniaxial isothermal hot compression test of AZ61 magnesium alloy was carried out on Gleeble-1500D thermal-mechanical simulator, the flow stress-strain curves and other information of dynamic recrystallization were investigated by numerical analysis. The relations between Z and other characteristic values of dynamic recrystallization, including peak stress, peak strain and grain size, were developed by regression analysis. The numerical simulation model of flow stress was introduced, its predicted values were proved to be close to the measured values with errors not more than 10%. The errors between predicted values and measured values for grain size were not more than 5%.