The energy spreading of recorded ions is influenced by straggling,geometrical acceptance angles and detector energy resolution effects in neutron depth profiling(NDP)and a symmetric Gaussian function model was customarily applied before.In addition,the spectra of mono-energetic alpha particles show a well known asymmetric shape as well when measured by silicon detectors.This article presents a physical model predicting the observed energy spectrum of a sample ion with target nuclides in prearranged depths.It is expressed as the convolution of a Gaussian function with a left-hand double-exponential function.Experiment showed that the predicted ions spectrum derived from the asymmetric model matches the observed energy spectrum.Therefore,the model can be applied to produce matrix for inversion of NDP spectrum. The energy spreading of recorded ions is influenced by straggling, geometrical acceptance angles and detector energy resolution effects in neutron depth profiling (NDP) and a symmetric Gaussian function model was customantly applied. Before addition, the spectra of mono-energetic alpha particles show a well known asymmetric shape as well when measured by silicon detectors. this article presents a physical model predicting the observed energy spectrum of a sample ion with target nuclides in prearranged depths.It is expressed as the convolution of a Gaussian function with a left-hand double -exponential function. Experimental showed that the predicted ion spectrum derived from the asymmetric model matches the observed energy spectrum. Beforefore the model can be applied to produce matrix for inversion of NDP spectrum.