To relax the requirement of the filter and reduce the control complexity of the SMPA, this paper proposes a 5-level RF-PWM method for all-digital transmitters with 3rd and 5th harmonic elimination. The method is achieved by changing the threshold signal to control the pulse width of the 3-level sub-pulses. Finally, the feasibility of the method is verified by simulation. For the 16QAM signal with a carrier frequency of 200MHz, the proposed method can achieve -46.24dBc and -54.05dBc respectively when the coding efficiency reaches 77.51%.