Recent advances in low-temperature thermochronology and its applications have shed lights on the detailed processes in the shallowest crustal depth (1~6 km), such as uplift, exhumation and cooling. This paper introduces a method of the Fast Fourier Transform (FFT) spectral analysis which is produced by Braun (2002b) , combined with the fractural thought to take the elevation(h)and AHe age(a)of samples as the input (I) and output signals (F); Then make a transformation from the time domain to spatial one by the FFT. Through it, the authors could inverse the last-stage of relief change of topography in the orogenic belt. Synthetically, this method considers the influence from the surface topographic fluctuation which could cause the isotherm to be curved.