In order to accurately measure the radiated emission caused by the pantograph arcing of EMU in the presence of environment electromagnetic noise, a transient electromagnetic signal extraction method based on sparse decomposition is proposed. Based on the Gabor atom library, an asymmetric Gaussian model is established by introducing an asymmetric parameter and an attenuation parameter, which makes the improved atom library more consistent with the asymmetric envelope and different attenuation rate characteristics of the pantograph arcing radiation pulses in the time domain. Based on the improved atomic library, the pantograph arcing signal is reconstructed by the sparse decomposition, thus realize the accurate measurement of pantograph arcing radiation. Simulation and laboratory experiments show that the method can effectively suppress the preecho phenomenon in the sparse decomposition based on traditional Gabor atomic library, and the reconstruction accuracy is higher; the denoising capability of the method under narrowband interference is about 17 dB higher than the denoising method based on EMD theory, and the error between the recovered transient signal and the original signal is within 3 dB.