An active absorption method based on multisize microperforated plate structure (MPP) is proposed in this paper. A separating panel which can be driven to move up and down horizontally is placed inside the cavity of MPP. The feasibility of adjusting acoustic impedance by moving the separating panel is discussed theoretically. The effects of two methods of driving separating panel on the three typical parameters multisize MPP are further compared by using the numerical simulation. For multisize MPP with a cavity of 15 mm depth, the average sound absorption coefficient at the band range of 800~1 900 Hz is up to 0.85. It indicates the validity of the active sound absorption method, and also provide a new way to widen acoustic absorption band of MPP absorbers.