While the high-volume low-concentration off-gas going through the adsorptive bed, the composition of VOCs would be adsorbed by adsorptive material and will be emitted up to the standard; At the same time the high-temperature air going through the saturated area namely regenerative area, the adsorbed off-gas would be desorbed to recover adsorbing ability of adsorptive material, and the formed middle-high-concentration low-volume desorbed off-gas will enters after treatment oxidation equipment to process oxidation treatment.