The invention discloses a power distribution network reliability quadratic optimization assessment method facing power distribution reliability. According to the method, a power distribution network reliability quadratic optimization assessment model facing the power distribution reliability is utilized, a weak link of the system reliability can be identified by upwards inferring the system model from a system layer, and then power distribution network reliability quadratic optimization assessment is carried out. According to the assessment method, the degree of influence on the system reliability from an element or an element assembly is represented through posteriori off-stream probability index and off-stream frequency influence degree index quantification. The method comprises the steps that firstly, a power distribution network is divided into a plurality of standard submodules, and then modeling and integration are carried out on the submodules; secondly, primary assessment on the index of the system reliability is carried out based on the model, and loading points and the index of the system reliability are obtained. The power distribution network reliability quadratic optimization assessment method facing the power distribution reliability aims to indentify the weak link of the power distribution network reliability and seek for an approach to improve the level of the system reliability.