In view of the irregularity and mutability of power quality transient disturbance signals， a new method for detecting the transient power quality disturbances based on sliding detrended fluctuation analysis is introduced. The correlated properties of the original signals change when a transient disturbances occurs， and the fluctuating parameters of the detrended fluctuation analysis are sensitive to them. Fluctuating parameter curves can be constructed according to sliding windows. It can detect the disturbance moment and determine the typical voltage fluctuation amplitudes such as voltage swell and sag. Experimental results show that the method is effective， and has better immunity to noise than the method based on wavelet transform.