The integration of power line communications (PLC) and wireless communications in power distribution internet of things (PD-IoT) provides a cost-efficient and easy-to-access solution to solve the problems of limited range of access and signal fading due to the influence of distance and obstacles. The traditional route selection methods are difficult to adapt to uncertain global state information (GSI) under dynamic network environment, the integration of PLC and wireless communications, and strong electromagnetic interference. In this paper, we put forward a state-action-reward-state-action (SARSA)-based Delay-aware Route Selection (SDRS) algorithm, which adopts software-defined networking (SDN) to simplify the network configuration and management in wireless-PLC PD-IoT. The proposed algorithm utilizes SARSA to evaluate and learn the optimal route selection strategy that can reduce transmission delay and improve reliability. Moreover, it can also adapt to the dynamic and complex communication environment. Compared with existing shortest route selection (SRS) algorithm and random route selection (RRS) algorithm, numerical results verify that SDRS has excellent performances in terms of transmission delay and reliability.