The invention discloses a fault diagnosis prediction system of a large-span railroad bridge based on PHM. The system comprises a visualization management module, an archival data module, an online monitoring module, an artificial polling module, a diagnosis prediction module, a maintenance module, a data interaction module and a PHM database. The invention further provides a fault diagnosis prediction method of the large-span railroad bridge based on the PHM. The fault diagnosis prediction system has the advantages that 3S network architecture, a BIM and a GIS technology are adopted to associate and archive design, construction, operation and maintenance information, by comprehensively monitoring trains, tracks, bridges, and bridge environments and processing big data of artificial pollinginformation, the diagnosis and prediction of bridge diseases and evaluation of health states of the bridge are achieved, and a decision-making basis is provided for the maintenance of the bridges.