Abstract: It has been emphasized in many literatures that diffusion is very important to the auditorium acoustics, but none of them has given a proper description on the sense of subjective evaluation of the auditorium. The acoustical parameters developed during past decades, such as EDT, C, LF, IACC are all related to the non-diffused sound field. The author presents an overview on this subject, and also points out some problems as what should be clarified and further investigated.