The invention discloses a furnace lining loss on-line monitoring system and method, the system is applied to a metallurgical furnace, the system comprises a data measurement module and a real-time calculation display module, the furnace lining temperature, the cooling water temperature and the flow can be measured, the furnace lining loss thickness can be calculated and displayed in real time, and meanwhile, the system also has alarm and remote communication functions. According to the invention, the furnace lining loss can be monitored in real time, and the safety and efficiency of furnace use are improved.