Through gasification and methanol synthesis, biomass can produce methanol and then produce light olefins through the methanol-to-hydrocarbon (MTH) process. To make this new biomass based production route profitable, the efficiency of the MTH process is important. Catalyst deactivation is the main reason for the decline of conversion and selectivity. NMR was applied to detect the relaxation and diffusion of liquid molecules in a series of coked ZSM-5, investigating the effect of coke on molecular transport properties. n-Heptane was chosen as a probe molecule in describing pore network connectivity, whereas methanol was used for relaxation measurements. Though there were only minor differences of pore connectivity among the samples, the longitudinal relaxation time showed an almost linear relationship with coke contents, suggesting that the interaction between reactants and catalyst surface influences the catalyst performance within low coke contents. PFG-NMR and NMR relaxation, as fast and straightforward measurements, could simulate catalyst behaviors during the reaction process.