With the access of Distributed Generation (DG) and the rapid development of the Active Distribution Network (ADN), network structure is becoming increasingly complex, frequent break faults seriously threaten equipment and personal safety and affect the stable operation of a power system. Because of the influence of DG, ADN break fault identification faces greater challenges, and there is still a gap in existing research. This paper proposes a single-phase break fault protection method for ADN based on negative sequence current. First, the characteristics of sequence currents and neutral voltage in the case of a single-phase break fault occurring in the upstream and downstream of DG are analyzed. The neutral voltage and negative sequence current are used as the protection parameters, and a single-phase break fault protection criterion for ADN with small resistance grounding based on negative sequence current is constructed. Theoretical analysis and simulation results show that the method is not affected by load distribution, fault location and network topology. It has high sensitivity, reliability, applicability and ease of implementation. This work is supported by the Joint Fund of National Natural Science Foundation of China (No. U1866603).