In this paper, a low-power synthesis algorithm is proposed. Based on polarity conversion technique, the minimal Mixed-polarity Reed-Muller (MPRM) expansions are searched with exhaustive algorithm. Then the corresponding MPRM circuits are decomposed in dynamic logic and the optimal power is gotten. MCNC benchmark circuits are tested and the results are performed with the Fixed-Polarity Reed-Muller (FPRM) circuits of the minimal power. It shows that the expansion and power are smaller in MPRM circuits, and the decrease rates are 47.8% and 29.6%, respectively.