In this paper the Fetri Net modelling of fauIt diagnosis and repair power distribution systems is studied. the main characteristics of modelling of t he systems is introduced and after the presentation of the main definitions of Petri Nets, a power distribution system is modelled. The system consist, of twenty two different states which are commonly divided into four groups naively: 1) Normal condition, 2) fauIt condition , 3)corupensated, and 4)after fault repairing. Different faults or irregular conditions, which may change the state of the system, are considered as the collection of different events. The model of the system is represented by the Petri Net graph and its evolution is simulated.