A method for driving a passive matrix organic light emitting diode (PMOLED) is provided. A pulse width modulation (PWM) constant current is provided to OLED pixels connected to a segment of a PMOLED array without voltage pre-charging the segment. Then, an offset value corresponding to missing gray scales of the OLED pixel is determined. According to the missing gray scales, the gray scales of the OLED pixel are rescaled starting from the offset. The OLED pixel is thus driven by a compensated PWM constant current having the rescaled gray scales during each horizontal line period.