In order to relax the filtering requirements and improve the wideband performance of the all-digital transmitters, a novel multi-level RF-PWM(radio frequency pulse width modulation) method for all-digital transmitters was introduced. This method limits the selective harmonics of RF-PWM signals by controls the pulsewidth of the corresponding subpulses to make the selected harmonics cancel each other out and keep the weighted superposition of fundamental frequency components proportional to input envelope. For the third harmonic elimination, the corresponding 5-level RF-PWM scheme was presented. And the optimal gain index for 5-level RF-PWM scheme was also analyzed and proved. On this basis, the proposed scheme was verified by extensive simulations.