The internal friction （IF）-temperature spectra of Ni49.8 Ti50.2 shape memory alloy at different oscillation frequency were measured with dynamic mechanical analyzer. The IF-temperature spectrum was quantitatively analyzed and decomposed into intrinsic and transitory sections using the iterative method. The relationship between the intrinsic IF spectrum and the frequency was also quantitatively investigated. The results indicate that the IF values decrease with the increase of frequency. The transitory IF-temperature spectrum at different frequency can be predicted from the calculated one at any other frequency based on the determined theoretical model.