The paper designs a 24 loops of the three-phase three-wire multi-function watt-hour meter based on MSP430 and ATT7022B. With the idea of time-sharing multiplexing, the MSP430 control three ATT7022B to actualize measurement and testing. The device not only can meet the requirement of detection, the accuracy of measurement, but also has advantages of simple structure and low cost. At the same time, the paper shows the whole structure of watt-hour meter, the module principle diagram of multi-loop voltage and current collection, the flow chart about software. Finally, the paper prospects the expanding application in future.