The invention discloses a microgrid fault reconstruction method and system based on an expert system. The method and the system are based on the expert system, an initial reconstruction scheme is obtained, and then is optimized on the basis of a microgrid maximum supporting force and network loss to obtain a reconstruction scheme, and the reconstruction scheme is stored in a case library in the expert system to improve the optimal solution ability of the system. By the microgrid fault reconstruction method and system based on the expert system, the circumstance that a topological structure needs to be subjected to load flow calculation when iterated every time can be avoided, the reconstruction efficiency is improved, a mode switching process of enabling a microgrid to run in an isolated net from a connected grid can be smoothened, the maximum load supporting force of the microgrid can be improved, and network loss is reduced.