A LED backlighting dimming method based on PDM algorithm was proposed in order to solve the defect of PWM dimming method in application.The frequency domain simulation analysis of waveforms showed that the harmonic frequency of PDM method moved to higher region than PWM method, avoiding the test frequency band（25 Hz~10 kHz）of CE101 so that it was easier to pass the EMC CE101 test with PDM method. As a result, compared with PWM method, the current waveforms were relatively gentle and the load characteristics were obviously improved by using PDM method. In summary, PDM method has advantages in electromagnetic environment and load sensitive applications.