Abstract: In order to understand the variation of fluid operation and internal composition in the steam generator of sodium-cooled fast reactor, the AR model of modern spectrum estimation and the periodic graph method of classical spectrum estimation, Welch improved periodic graph method and BT method are introduced to compare and analyze the original background noise data produced by the operation of sodium cooled fast reactor steam generator. The results show that AR model is more effective in estimating the background noise of sodium-water reaction.