Sensitive nonlinear iterative peak algorithms were discussed and applied to analyze the background of full-energy spectra of the γ-ray in this article.Under high-order filtering or at narrow windows

SNIP algorithms can restrain the influence of Compton scattering greatly and decrease the background effect of backscattering peaks

background peaks and characteristic X-rays from the shielding material

but this reduces full-energy peak counts.On the other hand

the full-energy peak counts become larger than the actual value using low-order filtering or at wide windows.By analyzing the conditions of SNIP algorithms

one can locate the boundary of peaks accurately.High analytical accuracy of specific activity of natural radionuclides can be achieved by SNIP algorithms with the filtering window changing in a large scale.The total relative error for measuring natural radionuclide specific activity of 238U

232Th and 40K is less than 8.5% using the fourth-order filtering at the window varying between 47 and 123.