The alternating detail parameter (ADP) is a new parameter to represent waveform microdistortion. It is proposed to overcome the shortcomings of the traditional evaluation parameters, the normalized correlation coefficient (NCC) and the variation trend parameter. This proposal is based on the principle that two discrete waveforms are more similar if the ratio of their corresponding differentials is close to one. ADP is shown to be correct by power spectrum analysis. Simulation research demonstrated that ADP is valid for evaluating the effect on the denoised partial discharge signal by associating NCC with signal noise ratio.