The invention relates to the technical field of electric energy quality monitoring of an electric power system, in particular to an electric energy quality monitoring system of distributed power supply access and a monitoring method thereof. A data acquisition module acquires monitoring data information; a wireless communication module transmits the acquired monitoring data information to a sub-data server for storage; the sub-data server compresses the collected monitoring data information to form a file index and then stores the file index into a main data server; and the file index can be called by each user terminal through a WEB server. According to the invention, online monitoring and analysis on the electric energy quality of a distributed power supply in grid connection are achieved; complex and changeable electric energy quality problems in connection of the distributed power supply to a power grid can be solved; by fully using the storage space and network bandwidths of eachserver, the storage space is saved and access efficiency is improved; and the system and the method has quite high reliability and expandability.