Distribution network information system uses domestic security algorithm, avoiding the possible back door trap that may exist in foreign algorithms. A national cryptographic algorithm SM2 for Modbus telegrams in distribution networks is proposed. The characteristics of distribution network information system are studied. The characteristics of the asymmetric encryption algorithm and the applicability of the national cryptographic algorithm SM2 in the distribution network Modbus are analyzed. On-line key management of distribution network information system based on SM2 is adopted. Digitally signing Modbus telegrams of distribution network based on SM2 to ensure the authenticity and non-repudiation of distribution network information are elaborated. The experimental platform to test the SM2-based key management and distribution network Modbus telegram exchange is set up. The test results show that the SM2-based distribution network information system can meet the security and real-time requirements at the same time. This work is supported by Science and Technology Project of Shanghai Electric Power Company (No. 52094015001V).