A Trichel pulse (TP) corona has been extensively studied by many investigators. From these results of investigations, it is obvious that the interval of each negative corona pulse is not constant and is fluctuating in time. This paper describes experimental results and the analysis at each frequency component of negative corona pulse in the VHF band. Because it is necessary to study the property at each frequency component in detail, Continuous Wavelet Transformation (CWT) was applied. However, in spite of such an idea no detailed study has been carried out up to now. From the obtained wavelet spectrum, it is clear that the generating mechanism of enhancement of TP corona due to accumulation of negative ion which tends to reduce the strength of the electric field and ionization zone in the near cathode region as increasing applied voltage.