The absorptivity of Micro perforated Panel Absorber (MPA) with the alterable air cavity,calculated by electro acoustic circuit approach (EC),exists the calculation error. The absorptivity is estimated by the impedance transfer method (ITM).The imaginary planes are adopted to divide the MPA with alterable the air cavity into several absorbers with equal width.The absorptivity of each absorber is calculated by ITM after the simplification of the model.By synthesizing the absorptivity of each sound absorption unit, the sound absorption coefficient of the whole structure is obtained.And the corresponding experiments are carried out.A comparison is made with the absorptivity calculated by ITM and EC.It shows that the theoretical results calculated by ITM agree well with experimental results,and is more close to the experimental results than the theoretical results by EC.EC is a kind of concentrated parameter analysis method. This method only considers acoustic compliance,while ignores the effect of acoustic mass.Thus it will cause calculation error.This kind of error does not exist in ITM and TMM,thus their calculations are more accurate than EC.