Based on the characteristics of the Ethernet passive optical network（EPON） and the requirements of the distribution automation， this paper presents a novel communication system for distribution automation using EPON. And the security threats to the proposed architecture are analyzed. By utilizing the symmetric cryptographic techniques and challenge-response mechanism， a secure communication scheme with encryption and authentication functions is presented， which conforms to the polling-based multi-point control protocol discovery process. The implementation details of the scheme are also described. supported by State Grid Corporation of China.