The application layer protocol for the new generation of interactive power line communications (PLC) needs urgently to be studied to support the intelligent services of the smart grid. In this paper, the architecture of PLC application layer and the application protocol data unit (APDU) are designed based on the users’ demand respond (DMR) and PLC technology features. The application services are then classified and an integrated service response mechanism adopting the dynamic priority is also put forward which is the core of the application layer. The superiority of the proposed application layer is verified on the platform of the cross-layer simulation with a practical PLC network in terms of transmission rate, package loss rate and transmission delay.