This paper proposes a smart distributed equalizer embedded with communication function for series-connected battery strings based on power and signal dual modulation (PSDM). The proposed equalizer can balance state of charge (SOC) of batteries and communicate with each other simultaneously. The control strategy of an equalizer is discussed to limit the SOC difference in a battery string. The modulation scheme, demodulation scheme and communication process are thoroughly presented. Finally, a four-battery three-equalizer system with a communication rate of 33.3 kbps is built to verify the feasibility.