In this paper the resistive mechanism of the device with structure of ITO/PMMA/Al and the relevant SPICE simulation circuit are investigated. By optimizing the annealing temperature of PMMA, the devices can achieve continuous erasable-readable-writeable-readable operation. Based on the surface morphology researches of PMMA with different annealing temperatures, a physics model of nonlinear charge-drift mechanism in doping system is established to explain the resistance characteristics of the organic device. And the state equations are established to describe the interface movement of different doping regions in the model. Then, the SPICE simulation circuit is set up with feedback control integrator. Finally, substituting the measured parameters of device into the simulation circuit, we obtain the current-voltage simulation curve which is in good agreement with the actual results of the device. The results verify the resistance mechanism of nonlinear charge-drift in our device, and the applicability of the SPICE simulation of nonlinear charge-drift model based on inorganic memristors to the organic resistive memory.