Prediction of breakdown voltage of transformer oil facilitates the early fault diagnosis and fault prevention of transformer.Since back-propagation（BP） neural network has prominent fault-tolerant

non-linear approximation

and self-learning capabilities

this paper presents a BP neural network with BP algorithm and a BP neural network with improved BP algorithm respectively to simulate the correlation between breakdown voltage and four relevant parameters

using the monitoring data of transformer oil.The results show the latter gives more accurate prediction values with a relative error within 5%.