Modeling of high-altitude electromagnetic pulse (HEMP) consists of one self-consistent process. Current density produced by Compton effects of gamma rays not only is the source in Maxwell's equation to produce electromagetic pulse, but also is influenced by electric fields. In this paper, analytical relation of Compton current and local electric field was deduced with reasonable hypotheses in one dimension model. It shows that self-consistent process is equivalent to an effective conductivity and can be combined with original non-self-consistent model. Analytical relation between Compton current and electric filed was verified using particle in cell and finite-difference time-domain methods. Finally, an example of HEMP environments calculated by this means was shown.