Packet-like space charge behavior is a kind of special transport behavior of space charge in polyethylene. It has been demonstrated that many factors, such as the intensity of applied field, temperature and material have great influence on the formation and migration of space charge packets. This would cause much difficulty in understaning the general mechanism of the phenomenon. In this paper, on the basis of analysis of charge injection and migration, the interaction between the charge and charge trap and the influence of electric field on charge trap level, a model is proposed to simulate the packet-like space charge behavior. We suppose thar there exists a negative differential relationship for the charge velocity against the electric field when the electric ficld exceeds a threshold value. By considering the negative differential relationship, we simulated various kinds of packet-like charge behaviors and the results of numerical simulation show a good agreement with the experimental results issued by different research groups.