The influence of potassium fluoride (KF) on the in-situ sealing pores of plasma electrolytic oxidation (PEO) film on AM50 Mg alloy has been investigated using a stereo zoom optical microscope, scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS). The films formed in the solutions with and without KF were compared. The sketch map for the formation process of in-situ sealing pores was established. The in-situ sealing pore PEO film can be obtained in the solution with KF, while the PEO film with open pores is obtained in the solution without KF. It indicates that the addition of KF plays a key role in the formation of in-situ sealing pores. Moreover, KF can change the initial film and promote the film growth rate. (C) 2015 Elsevier B.V. All rights reserved.