This invention publishes a fault diagnosis and location system for transformer core looseness, consists of vibration sensors, data collection and computer. It is of power transformer fault intelligent diagnosis technology technical field. Fault diagnosis and location method uses three vibration sensors positioned on the top of transformer tank, to obtain vibration signal, uses signal processing to analyze the signal, and obtains fault characteristics of the transformer core looseness. The characteristics respectively are 50 Hz, 150 Hz and 300 Hz frequency components, in which 300 Hz is main feature. When they reach a certain value at one position, it suggests that transformer core looseness near this position. By the comparison of differences among signals of three positions, fault location can be done. This invention manifests fault characteristics accurately and detects core looseness efficiently.The invention uses the electricity grid frequency of 50 Hz for example, for 60 Hz power system, above 50 Hz, 150 Hz, 300 Hz characteristic frequencies are 60 Hz, 180 Hz and 360 Hz.