Abstract: The composite algorithm proposed by Stein and Scott was improved, whose weight factors were optimized by the weighting factors proposed by Kim et al, and whose coefficients of weighted dot-product similarity measure and peak ratio algorithm were redistributed. Using the improved composite algorithm, 30 932 mass spectra in the query library were retrieved in the Mass Spectral Library 2011 (NIST 11) main library (212 961 mass spectra) used as reference spectral library. In addition, 8 kinds of different compounds were analysed by gas chromatography-mass spectrometry (GC/MS), and the corresponding mass spectra were also retrieved in the NIST 11. In order to evaluate the performance of the algorithm, two different sets of experiments were carried out, and the accuracy and similarity of the query spectra or the experimental samples were analysed by using two combinatorial algorithms respectively. The results showed that compared with the previous composite algorithm, the accuracy of the query spectra matching in the reference spectral library was increased by 1.15%, and the similarity of the 94.45% of the mass spectra in the query library were improved. The spectrum of the sample through the GC/MS had higher hit rates in the reference spectral library, and the spectrum similarity increased 3.56% in average. Since the improved composite algorithm can improve the accuracy and similarity of the spectrum to be measured in the reference spectral library, it can also be used to improve other algorithm based on Stein and Scott’s composite algorithm.