An equivalent model for distribution system is presented

which takes the least distribution sections as analytic elements to significantly simplify the components calculation.The describing matrix of network based on the sections model is proposed

with which all fault node sets can be quickly classified.Moreover

generalized matrix formulas for evaluating reliability indices of a distribution system are deduced.The algorithm takes sufficient special factors into account

such as misoperations of fuses or breakers

and multiple adjacent sources in network

and respectively assigns the parameters of overhead lines or cables

according to the actual situation.Example results show applicability and effectiveness of the algorithm.