This study presents a novel model that combines the tank-in-series model and the random replacement IEM (interaction by exchange with a mean environment) model for investigating the effects of both imperfect micromixing and macromixing. Two unstable chemical reaction model systems are simulated, the Oregonator model and the pH oscillator model. Dynamical behaviors include steady state, relaxation oscillation, small oscillation, and chemical chaos. Simulation results revealed significant effects of mixing; however, the ways the system dynamics had been altered depended on the chemical reaction systems.