Abstract: The changes of the gaseous components dissolved in transformer base oil under thermal stress at low temperature were investigated by gas chromatography method. Test results show that under the conditions of transformer base oils having various aromatic contents and from different crude base, prior and post to vacuum degassing, the contents of dissolved gases in oil are related with the content of dissolved oxygen in oil, storage temperature and storage time directly. Prior to vacuum degassing, the contents of dissolved gases increase with the increase of aromatic content in oil; post to vacuum degassing, the contents of dissolved gases not seem to be had direct relationship neither with aromatic content nor crude base.