The linear power flow calculation method can improve the robustness and rapidity of the centralized optimization control of active distribution network. With the wide access of distributed generation in active distribution network, voltage control nodes in distribution network gradually increase to maintain normal voltage level. Existing three-phase linear power flow under a rectangular coordinate system cannot cope with local voltage control nodes, the existing linear power flow model under the polar coordinate system failed to consider detailed control characteristics of DGs, network loss allocation and three-phase characteristics of distribution network. Therefore, this paper proposes a linear power flow calculation method in the three-phase polar coordinate system to solve the problem. The proposed method considers the types of Y-connection ZIP load, Delta-connection ZIP load and single-phase or three-phase Distributed Generators (DGs), etc. DGs detailed control model and distributed slack bus model are also considered. Finally, the proposed method’s accuracy and adaptability of various node types are verified by the three-phase unbalanced IEEE 13, 34, 37 and 123 nodes system. This work is supported by Science and Technology Project of State Grid Jiangsu Electric Power Co., Ltd. (No. J2017013) and National Natural Science Foundation of China (No. 51707196).