This paper uses direct Monte Carlo simulation method to predict the process of gaseous chemical reaction. The paper studies the dissociation reaction of gaseous molecules, discusses the reliability of extrapolating chemical reaction rate from lower-temperature region to higher-temperature region through Arrhenius empirical relation-ship obtained by experiments under lower-temperature condition, analyses the effects of thermal nonequilibrium on chemical reaction rate，and presents the relation between chemical reaction rate and gas temperature obtained through direct Monte Carlo simulation method.