Abstract: Based on preliminary experimental results in the work'Experimental investigation on sound absorptioncharacteristics of microperforated absorber in diffuse fields'.Sound absorption characteristics of microperforated ab sorber in diffuse fields are further investigated.Sound absorption characteristics in diffuse fields are similar to in normalincidence with a frequency shift when the perforated constant k is large (k>2).While k is small (k ≤ 2),Soundabsorption characteristics of absorber in a diffuse sound fields are shifted to higher frequencies as well,but additionalabsorption at higher frequency due to the secondary absorption band as a result of mutiple-branch of the cotangentfunction becomes more and more importallt and finally takes over the role of principle factor of the absorption.As aresult,the absorption band may extend to three,four octaves or more.Calculations were made and explanations of theresults offered.