The invention discloses an extension cone method capable of sensing the real-time situation of a power distribution network. According to the extension cone method, an extension cone planning model is established, real-time trend results such as the voltage amplitude value and the phase angle of nodes of the whole network are calculated, and the purpose of sensing the real-time situation of the power distribution network is achieved. The extension cone method comprises the following steps that first, net rack data are read, the net rack data comprise the connection relation of the nodes and branch circuits, real-time data returned by points which are provided with measuring devices and historical loads of points which are not provided with the measuring devices; second, a planning mathematical model is established, the planning mathematical model comprises an objective function model, a trend equation equality constraint, an inequality constraint of node voltages and load nodes; third, secondary cone planning processing is conducted on the trend equation equality constraint, the node voltages, node active power and node reactive power respectively, and state estimation models of an objective function, the equality constraint and the inequality constraint are obtained; fourth, the state estimation models are solved, so that the voltage amplitude of the nodes of the power distribution network and the trend information of the phase angle are obtained, and the purpose for sensing the real-time situation of the power distribution network is achieved.