The surface roughness and morphology of the ceramic coatings fabricated on industrially pure aluminum by the plasma electrolytic oxidation (PEO) technique with a hetero-polar pulsed current ceramic synthesizing system were investigated. A model for the process was established. Based on this a formula was deduced to estimate the temperature rise rate at the corresponding locations before the plasma discharge channels have formed during the PEO process, and the channels’ temperature when the plasma discharges occur. Results show that the PEO ceramic coatings grow by an alternating coating melting and solidifying way; The coating roughness becomes greater and the plasma discharge channel population in the ceramic coatings decreases while the pores enlarge with PEO treatment time and current. With the deduced formula, the PEO alumina coating on industrially pure aluminum was taken as an example for validation of the model.