Independent component analysis (ICA) has demonstrated its power to extract mass spectra from overlapping GC/MS signal. However, there is still a problem that mass spectra with negative peaks at some m/z will be obtained in the resolved results when there are overlapping peaks in the mass spectra of a mixture. Based on a detail theoretical analysis of the preconditions for ICA and the non-negative property of GC/MS signals, a post-modification based on chemical knowledge (PMBK) strategy is proposed to solve this problem. By both simulated and experimental GC/MS signals, it was proved that the PMBK strategy can improve the resolution effectively.independent component analysis (ICA), post modification, immune algorithm (IA), GC/MS Gas chromatography mass spectroscopy (GC/MS) is now a powerful tool to qualitatively and quantitatively analyze the composition of mixtures, especially the practical complex samples. The overlapping chromatographic peaks, which are generated by the incomplete separation in column, are often observed in practical analysis, since the compounds in such systems are complicated and often similar in properties. These overlapping peaks may affect the qualitative analysis by mass spectral information and worsen the quantitative measurement by chromatographic peak area, and sometimes even make the analysis completely impossible. Despite experimental and technical efforts to improve the separation efficiency, many chemometrical tools have been developed to obtain the spectral information and the corresponding concentration profiles directly from the overlapping chromatographic peaks, such as principal compo nent analysis (PCA) [1,2] , chemical factor analysis (CF-A) [3][4][5] , multivariate curve resolution techniques [6,7] , immune algorithm(IA) [8][9][10] , wavelet transform (WT) [11][12][13][14] , etc.In recent years, independent component analysis (ICA) [15][16][17][18] was greatly developed as a potential statistical technique for blind source separation (BSS). ICA was firstly applied to solving the cocktail party problem. It concerns that m receptors, i.e., microphones, are used to record the mixed speech signals from n sources, i.e., the speakers, in a cocktail party. Through making full use of the high-order statistical characteristics of the source, i.e., the fourth-order central moment, ICA can effectively estimate the independent components from their linear combinations without any additional information about the source signals. This method is now widely applied in the signal processing fields, such as biomedical signals [19] , image processing [20] and financial