The study of the potential decay in dielectric materials has a long history and is closely related to the wide application of corona charged dielectrics. One of the phenomenon that has an important influence on potential decay is the observation by Professor Ieda in 1967. His results were that in particular circumstances polyethylene potential decay curves with several initial charge levels did cross each other. This crossover phenomenon has been scoped in many works and excited theoreticians imagination. Many models about the potential decay have been published but no more experimental results to prove the hypothesis. This project aim is to utilize the space charge measurement technique to explain the crossover phenomenon and moreover to find physical mechanism through observing the charge decay process in a corona charged polymeric material. The anticipation is that the application of this charge mapping technique may shed more light on the mechanism of charge decay. As we know if the deposit charge can inject and transport from the bulk of charged sample, there should be an acoustic wave detected by the sensor because the charge will move under the columbic force produced by the narrow and high voltage pulse. If some signals detect by the oscilloscope, there should be charge inside the bulk of sample. If the charge distribution in the sample is observed, there will be experimental evidence for the research of charge injection, transport and storage in the dielectrics. One essential phenomenon; bipolar charge injection has been derived from charge distribution results. By combining both surface potential of two layers LDPE and space charge measurement, direct evidence has been found to support the theory that the bulk transport process is accountable for the surface potential decay. Charge mapping technique (PEA) was successfully introduced to the potential study. This provide an alternative way to investigate charge decay process and allows monitoring charge migration through the bulk of corona charged film.