Abstract: The prevalent linear thermodynamic expressions of irreversible process are just available to those physicochemical changes which are close to equilibrium. On the other hand, the studies on the physicochemical changes far from equilibrium are mainly focusing on dissipative structures. A nonlinear dynamic equation is therefore set up for the chemical reactions far from equilibrium by way of extending the linear expressions to the homogeneous single chemical reaction systems far from equilibrium with no dissipative structure involved. The equation has been applied to water-gas reaction with a quintic expression obtained in high conformity to measured data with a maximum error of 8%. The result reveals that in such a way the thermodynamics of irreversible process can be applied to homogeneous single chemical reaction systems far from equilibrium.