In this article, we established a theoretical model that can describe the voltage-current characteristics of resistive memory devices, containing a layer of the organic polymer semiconductor material sandwiched between two electrodes. We found that the rise of HOMO level of Donor-Acceptor polyimides due to the structure change from ground state to excited state reduces the hole injection barrier between cathode and polymer, leading to the enhancement of the electric current. In other words, the applied external field stimulates the polymer to the switch from OFF state to ON state. We can simulate the I-V curves in excellent agreement with the experiment results by using electrical property of ground state and excited state for simulating the low conductivity curve and high conductivity curve, respectively. Furthermore, we can obtain a reasonable ON/OFF ratio by simulation. The logarithm of ON/OFF ratio and △HOMO exhibit a linear correlation. Therefore, the ON/OFF ratio of new polyimide materials can be predicted by calculating the change in the HOMO level between the ground and excited states.