The adsorption dynamics of perfluoroisobutene (PFIB) on fixed bed activated carbon under various humidity conditions was studied, and the granular activated carbon was treated using a microwave. The equilibrium adsorption capacities and adsorption rate constants were calculated using the Wheeler equation. The dynamic model based on linear equilibrium was used to correlate the entire experimental data, and the theoretical breakthrough curves of PFIB on the carbon bed were then obtained. The results showed that the pore structure did not change obviously, but the surface oxygen content decreased after microwave modification. The selective adsorption capacities to PFIB increased greatly, and the carbon bed's effective protection time against PFIB was prolonged under high airflow humidity. The theoretical breakthrough curves agreed with the experimental data very well, and this kinetic model can be used to predict the breakthrough behavior and to design and select the parameters of the respirator cartridges.