Abstract: Two calculational methods for analyzing the spectrum which measured by indoor low background multi-channels gamma-rays spectometer(Na(Tl)) to get the specific activity of 226Ra, 232Th and 40K of the sample are discussed, they are the spectrum analysis method and the characteristic energy peak method(inverse matrix method) respectively. The sample spectrum are analyzed with the program designed according to the two methods, and compared with the results by HPGe gamma-rays spectrometer, showing that the relative deviation is ≤10% with the two methods.