The invention relates to a power system partition reliability evaluation method. The method comprises the steps of inputting the data of a to-be-evaluated power grid, marking the partition of a power system in a power grid topology structure to respectively marking out five regions in the power system, grading the rates of the five regions according to the sizes of loads, evaluating the reliability of the power grid at all voltage levels based on the Monte Carlo Simulation method, recording the result of the reliability evaluation, conducting the statistics on the accident information in each region according to the result of the reliability evaluation, classifying accidents based on the two standards of the out-of-load ratio and the power-outage user ratio, calculating the accident risk index value of the power grid, and adopting the obtained index value as the result of the reliability evaluation in each region of the power grid. According to the technical scheme of the invention, during the planning and running stage of the power grid, the risk levels of the power grid at different accident levels can be evaluated, so that improvement measures are conveniently and correspondingly provided for the power system. Therefore, the risk of the system is reduced. Meanwhile, the power supply capability of the power system is improved.