The invention belongs to the technical field of power system measurement, and particularly relates to an online load analysis and modeling system and method for a power system. The system comprises adata recognition module, a load modeling data integrity checking module, a load analysis module, a load modeling module, a fault recording management module, and a fault fitting automatic adjustment module, collects the model data, network topology data and real-time data of a transformer substation and a power distribution network provided by a power dispatching technology support system and a power distribution automation system on line and the industry load classification and load actual measurement data provided by a marketing comprehensive data platform, and realizes the online load analysis and modeling functions of the load nodes by combining the load classification situation of a modeling system and adopting a comprehensive aggregation equivalence method. According to the present invention, by adopting the normalized load analysis and modeling work, the timeliness and accuracy of the load modeling are improved, the safe, reliable and economical operation of a power grid is guaranteed, and the implementation difficulty and workload of the load analysis and modeling are effectively reduced.