In order to improve the operating economy and safety of coal-fired power generating units, the remote diagnosis of regenerative system fault was carried out.By establishing the calculation model of steam extraction and heat return system, the performance of all levels of heaters was analyzed, and the problem of low feed water temperature of unit was diagnosed remotely.The results show that the extraction parameters of the regenerative system do not match well with the performance of the heater. The temperature rise of several heaters has not reached the design value, especially the No. 2 high pressure heater. The accuracy of the analysis and judgment was verified by the equipment disassembly and maintenance. After the problem was solved, the water supply temperature of the unit was increased by 3.2℃, which improved the operation economy of the unit.It is concluded that it is of great engineering practical significance to carry out remote diagnosis of unit faults based on big data and effectively alleviate the problem of low feed water temperature of the unit.