Abstract: The invention provides an intelligent assessment method of main insulation condition of transformer oil paper insulation, comprising: establishing at least one standard states; for each standard state, performing accelerated thermal aging tests on a plurality of samples to place the samples in the standard state, wherein each of the plurality of samples undergoes the accelerated thermal aging tests for different time periods; extracting time and frequency domain characteristic parameters of each of the plurality of samples; forming a feature vector using the time and frequency domain characteristic parameters of each sample, and forming a knowledge base from feature vectors of all samples; training a classifier by using the feature vectors of the knowledge base; and assessing the main insulation condition by using the trained classifier.