This paper developed a comprehensive model which can fully explain the surface potential behavior of corona charged organic dielectric electrets. Compared to previous studies, both sides of the corona charged films were measured while they were grounded or free-standing. All films showed surface potential with the same magnitude, but opposite polarity on each side while they were measured with the other side grounded. This indicates that in contrast to the previous incomplete model, believing only the corona side containing injected charges, both sides should contain injected charges with the same magnitude but opposite polarity. This dipolar charge distribution is relatively stable and leads to a constant and controllable potential difference ΔVf between each side of the free-standing measured film. Interestingly, free-standing surface potential varied dramatically for films charged with the same parameters. This large variation is caused by the minor number of free charges, which is only ~0.1% of the corona induced dipolar charges. Therefore, in this model, dipolar charges control the surface potential difference between each side and the minor charges control the absolute value on a certain side. By manipulating them together, the surface potential on both sides can be precisely controlled.