Abstract: In perceptual audio coding with low bit rate application, the pre-echo artifact is more distinct, and the effective detection of transient signals is the precondition. Transient intensity is defined in term of the Peak-Mean power Ratio(PMR), accordingly, a novel detecting algorithm of transient signals on time domain is presented while PMR is used as a criterion function. Because of considering the temporal masking effects to set up a threshold and the valid hop size of transient points, this method is very suitable for perceptual audio coding. When compared with the typical perceptual entropy detecting on frequency domain，it has some advantages, such as higher time resolution, more accuracy and simple algorithm.