Abstract: The urban power grid of China is evolving to smart distribution network progressively, of which the operation circumstance will be more complicated. Distribution system security region（DSSR） is a new concept for guiding the safety operation of distribution system. This paper studies the smart DSSR from the traditional view of load, taking two main elements of smart distribution system into account: distributed generator（DG） and demand response（DR）. Firstly, the characteristics of security for distribution systems with DG and DR is analyzed. Then the mathematic model of DSSR with DG and DR is built.Secondly, the effect mechanism of DG and DR on DSSR is studied by observing the diagram of two-dimensional sections for DSSR of the case, and based on which the guidance for planning and operating the system is proposed. The view of the load for proposed DSSR in this paper is consistent with the usual practice of dispatchers and can be a useful analysis tool of real-time security operation for urban distribution network, which gives first place to load supply and give second place to DG and DR service.