In order to study the influence on the distribution system when distributed generator(DG)is accessed

probabilistic load flow based on the total probability theory is proposed. An improved probabilistic model of DG is established. Meanwhile the random failure of transmission lines is also taken into account. The security risk of the system is quantified and the drawbacks of the system are distinguished through a two-stage(nodal and systemic stage voltage off-limit and loss of load)risk index created. The calculation results provide the basis and support for the planning of DG. The correctness and feasibility of the proposed methodology are tested by an IEEE 33-bus distribution system with DGs. This work is supported by Fundamental Research Funds for the Central Universities(No. XJJ2015034).