Smart grid applications need timely and reliable data communication systems, but the traditional fiber optic wireless sensor network (Fi WSN) system may not meet its short delay requirements. Therefore, a digital intelligent communication mechanism (XWMOC) for passive optical network (PON) based on the quality of service (QoS) mechanism is proposed in this paper. Firstly, cooperate with optical network units (ONUs) through wireless communication networks to reduce latency while avoiding interference from external devices. Secondly, the cross layer interaction between the application layer and the medium access control layer (MAC) can reduce packet delay in wireless sensor networks. Finally, by introducing service differentiation into the optical encoding ONU through two priority queues, the ultimate communication rate and reliability improvement can be achieved. Based on the above method and combined with user data from relevant regions of State Grid Chongqing, the research experiment on remote protection and synchronizer was conducted using the IEEE 802.15.4 standard. The experimental results show that the mechanism proposed in this paper can realize digital intelligent communication of power grid, reduce the end-to-end delay in Fi WSN system and long-distance passive optical network (LR PON), and provide a more efficient and reliable data communication system for smart grid applications.