Abstract: By analyzing the characteristic of the electric field change meter in both time and frequency domains, a new method by using transfer function to understand the electric field change meter is proposed. Analyzing of the transfer function indicates that the output of the field meter can be viewed as a high pass (HP) filter on the external E-field changes, which parameters are determined by the area of the plate and the time constant of the circuit. Based on these, inverse filter and HP filter methods are designed to recover external E-field changes and transform output signals between various E-field changes meters. Finally, these methods are applied to the observational data of an IC flash. Processed results are in good consistency with the observational waveforms, which demonstrates the feasibility of the methods. The filter methods unify the current fast and slow antennae, and bring forth new thoughts to measure lightning electric field changes.