The intelligent online monitoring device for oil-immersed current transformers enables real-time intelligent monitoring. It displays or transmits data on abnormal conditions before a fault occurs in the oil-immersed current transformer, such as rising oil levels in the expansion tank, increasing internal pressure, rising temperatures, and abnormal gas content in the insulating oil. The device intelligently determines whether the state parameters are normal based on threshold values, achieving intelligent online monitoring of oil-immersed current transformers.