With increasing penetration of distributed generation (DG), the overload of feeder lines and out of voltage limits will happen in distribution networks, which may limit the penetration of DG. Demand response can promote large-scale DG accommodation by utilizing demand side resources to participate in active distribution networks (ADN) scheduling. Therefore, a price-based demand response model is introduced to the existing multi-period optimization model for ADN, an active and reactive power coordinated economic dispatch model of three-phase ADN is developed and its solution method based on mixed integer second-order cone programming is proposed in this paper. The proposed model can reduce loss and ensure that the overload of feeder lines and out of voltage limits will not appear via optimizing the operation of DG, energy storage system and VAR compensation as well as demand response load. Simulation studies on the modified IEEE 33-bus system are presented to verify the effectiveness and advantage of the proposed model.