An evolution of a homogeneous chemical reaction system is described by a set of nonlinear ordinary differential equations. When the evolution occurs on different time scales, a special singular perturbation method may be employed to extract the equations for the slow evolution. The resultant equations have a quite simple form and retain high accuracy in the solutions. For illustration, an H-2/O-2 oxidation model is treated by this method. A general reduced model containing no radicals has been obtained, which can be applied to a wide range of initial conditions and has very good accuracy for the temperature and all the species.