Operation performance and condition monitoring of AC relay in power transformer cooling equipments is vital to the safe and stable operation of a large power transformer. Regarding as the incorrect issue of performance parameters of AC relay based on the traditional extracted method, an extracted method is proposed by using the fast amplitude calculation method of alternating current voltage signals combined the wavelet denoising part in this paper. By simulation on the fast amplitude calculation method of alternating current voltage signals and the testing and comparison on the practical AC Relay for a power transformer cooling equipment, the results and comparison have shown that by adding the wavelet denoising part, the proposed performance parameters extraction method of AC relay has better availability and accuracy.