This paper analyzes the recent development and standardization of narrow-band OFDM technology for low-voltage power line communications(PLC) targeting automatic meter reading and management (AMR/AMM) applications. The pager first introduces the characteristics of low-voltage power distribution lines when used as communication channel, and reveals the reason way OFDM(Orthogonal Frequency Division Multiplexing) has been widely adopted for the new generation of PLC. The paper then proposes a protocol stack model for the local PLC in AMR/AMM system to establish a layered framework for standard development to realize interoperability. Based on this model, the paper finally focuses on the PLC physical layer, analyzes the necessity of zero-crossing transmission, and performs a comparison of the main narrow-band OFDM PLC standards.