To address the issue of information islands in the visible light communication technology (VLC) and improve the communication requirements of the uplink, power line communication (PLC) is used as an effective supplement for the traditional VLC and enables connection to the uplink backbone network while supplying power. To assure the efficient transmission of signals in the two-level channel of the PLC and VLC technology cascade system, central node demodulation and modulation (CNDM) model based on orthogonal frequency division multiplexing (OFDM) is proposed in this paper. According to the multipath fading of PLC and the reflection properties of VLC, the channel model of the cascaded system is developed. Combined with the signal characteristics of OFDM and the cascaded system, the transmission strategy of a direct current biased optical OFDM system appropriate for both PLC and VLC is devised. To suppress the cascaded channel interference effectively, a multisegment joint control signal frame structure is designed. The experimental results show that under the simulation conditions, the cascade system may satisfy the communication requirements using various modulation schemes with acceptable signal quality, and the low bit error rate can reach 10^-4. Under the real-world measurement conditions, the cascade system can successfully transmit and receive signals reliably, with an overall minimal bit error rate of 0.