Abstract: To research the properties of transient electromagnetic signals radiation field from various radiation sources, the cylindrical conductor transmission line is modeled. The far radiation field of corona discharge is calculated based on frequency domain method. The calculated results indicate that as the length of conductor elongating, attenuation time of discharge signal increases, and the discharge components in high frequency decrease. The measurement experiment of transient electromagnetic signals is conducted, which verifies the calculated results. Meanwhile, the time domain and frequency domain frequency information of sparking from motorcycle spark plug are measured. The measured results show that properties of spark discharge are the same as corona, but different in frequency spectrum. The frequency spectrum of discharge could reach upon GHz.