A computer-aided searching program has been designed to analyze electron impact mass spectrum, First original data and the molecular weight were inputted. If the relationship of Z(son peak) +Z(neutral fragment) =Z(mother peak) -1∩Z(son peak)≥Z (neutral fragment), where Z means unsaturated bond number, is satisfied, all possible molecular formulas with corresponding bond-breaking rules, all possible element formulas of all peaks, and the neutral fragments can be obtained. To examine this program, 17 examples, whose corresponding data were all known, were tested. The results turned out to be all correct. Therefore this analysis program is trustable.

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