The invention provides a power grid automatic partitioning method based on a linear weighing method. The method provided by the invention includes establishing a model containing a transformer substation, a power source, circuit information nodes and edges; setting a node active power matrix; setting weighing coefficients of a broken ring line number and broken ring line power flow; according to transformer substation geographic positions, selecting two transformer substations that are least likely in the same area and classifying the nodes corresponding to the two transformer stations into the two areas; solving a linear weighing method based power grid automatic portioning function and obtaining an initial portioning scheme minimizing the broken ring line number and the broken ring line power flow; calculating short circuit current and the like in the areas in a final portioning scheme. According to the invention, the broken ring line number and the broken ring line power flow are taken into consideration fully. Line utilization efficiency is improved as much as possible under the premise of meeting requirements for short circuit current level. Blindness of performing power grid partitioning depending on experience is avoided and a powerful support is provided for stable, safe and economical operation of a power system.