Abstract: Distribution networks will serve as a comprehensive energy platform for the future society. The characteristics in the source, network, and load are changing more and more dramatically, bringing great challenges to the coordinated planning of distribution networks. The paper focused on the coordinated planning of smart distribution networks with consideration of the source-network-load evolutions. The driving forces for the development and evolution of distribution networks were analyzed. The influences of multiple driving forces on system planning were discussed. Several key issues were elaborated, including the morphology feature extraction and quantification, dynamic aggregation and prediction of planning elements, planning under complex scenarios, and multi-scenario deduction and decision-making. Analysis of the composition, objective and research direction of the key issues were performed, providing some thoughts and references for the development of smart distribution network planning technologies.