Aiming at the path loss and signal collision problems encountered in wireless networking in complex environments, a lightweight LoRa relay network based on Beacon-Coordinated Dynamic Time Division Access (BCD-TDA) mechanism was proposed. In this scheme, the static networking between the gateway and the relay nodes is realized by Frequency Division Multiplexing (FDM), and the downlink instructions are dynamically scheduled by dual priority queues. For end-node access, the communication cycle is innovatively divided into registered/unregistered windows, and collision-aware dynamic waiting time allocation is implemented through the Time Division Multiple Access (TDMA) token generator. MATLAB simulation results show that compared with the traditional ALOHA protocol, Slotted ALOHA protocol, and BCD-TDA demonstrate faster convergence speed, support second-level registration response in small-scale networks, and support dynamic node access. This scheme only needs a single-channel LoRa module to complete the relay function, which can effectively reduce the cost. It provides a new idea for the field of environmental monitoring of low-power Internet of Things.