Abstract: Acoustic structure study always is the research interest of the academic area. Diffusion absorbing structure (Diffsorber) has good research value because it has both diffusion and sound absorption property. Quadratic residue diffusers (QRD) structure which had good diffusion property was combined with perforated plate which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-plates which had 1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams and diffusion coefficients of different structures were derived and analyzed. Results showed that the composite structure still had good diffusion performance in the frequency range from 100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated plate resonance frequency range where there was about 2 dB reduction averagely. The study result can provide the reference for the design and development of diffsorber.