The DSM (Delta-Sigma modulator) can get a better performance by increasing the quantizer′s levels. But the multi-bit DSM output cannot drive the SMPA (switch-mode power amplifiers) directly due to the multi-levels of DSM output in the class-S DPA (digital power amplifier). So the multi-level SMPA with multiple SMPA cells is needed. Several level synthesis strategies for 4-level class-S DPA based on 2 bit DSM were proposed and analyzed. The theory and simulation results show that, with an appropriate level synthesis scheme, the 4-level class-S DPA obtains a much better performance. Especially, the effect of level synthesis strategy is more remarkable in power back-off condition.