The EMC accordance in Power Electronics (PE) equipment depends more the character of the semiconductor devices who work as the switchers than in other electronic equipment because the switching of the semiconductor device in PE may be the main cause of EMI. This paper proposes a novel approach that acquires PE equipment signal waveform by an oscilloscope, and analyzes the signal with Continuous Wavelet Transform (CWT), which can diagnose device's characteristics effects on equipment EMI. The algorithms of proposed approach are given followed by a case study, proving the feasibility of the proposed approach.