A broadcast/communication convergence system and method for transmitting and receiving Ethernet data by an optical network unit (ONU) performing a time division multiplexing (TDM) operation and switching by a network switch. A resultant signal is transmitted to a corresponding subscriber set-top box (SSTB), and data from the SSTB is provided to the network switch. A length of an Ethernet data frame is provided from the network switch, and an encapsulation generates and inserts data length information into an Ethernet data frame, for transmission to the SSTB. The SSTB carries out a TDM operation for a signal transmitted from the ONU, and separates the signal into Ethernet and broadcast data. A framing bit is detected based on a result of the separated signals, the length information is detected. A preamble bit and a start-of-field delimiter (SFD) are inserted into the recognized Ethernet data to recover the original Ethernet data.