The invention discloses a protection device reliability online prediction method and system based on a prudential system. The method comprises the steps: determining an abnormal state space which canbe monitored by the prudential system, wherein the abnormal state space is composed of varieties of abnormal states, and the prudential system is used for collecting operation data of a protection device in real time; determining occurred abnormal states of the protection device, an abnormal frequency of the occurred abnormal states and abnormality duration time according to the protection deviceoperation data collected by the prudential system; obtaining a markov state space method model; determining abnormality possibility of all kinds of abnormal states according to the markov state spacemethod model and the abnormal frequency and the abnormality duration time of the occurred abnormal states. The protection device reliability online prediction method and the system based on the prudential system disclosed by the invention can accurately and automatically finish real-time online prediction on the abnormal states of the protection device and further have the characteristics of saving labor and strong reliability.