A deactivation study of ZSM-5 in heterogeneous catalysis during the pyrolysis of a biomass-derived compound has been carried out. Experiments were performed in a gas-solid reactor with an online weighting system at varied temperatures, weight hourly space velocities, and partial pressures. Real-time catalyst weight monitoring during the catalytic conversion of furan as a main intermediate of biomass fast pyrolysis can be realized. The coke amount increased from 3.48% at a temperature of 300 degrees C to 9.81% at 700 degrees C and then declined slightly at 800 degrees C. The catalyst weight increment included active carbon species confined in the catalysts and inert carbon species of large unsaturated carbon molecules, which were defined as active coke and inert coke, respectively. Differentiation curves among displayed coke amount, active coke, and inert coke were described. Active coke accumulated quickly at the early stage; meanwhile, inert coke was dominant for its suppression on the catalysis reaction at the later stage, along with a slight decrease of active coke, namely, part of active coke was converted to inert species. An empirical and intrinsic model has been developed via an iterative process of model formulation, parameter estimation, and model validation with a final correlation coefficient of 0.968. To determine the kinetic parameters, several supposed deactivation functions F were introduced to the Arrhenius equation in a temperature-programmed reaction. Finally, a possible coking network was provided by introducing a multilayer theory, in which inert coke was supposed to be formed only on the surface of a microporous catalyst layer by layer.