Abstract: Study and Application on the Compositive Pattern and the Distribution of Molecular Formulas of Organic CompoundsCong Puzhu(Institute of Medicinal Plant Development,Chinese Academy of Medical Sciences, Beijing 100094,China)Abstract:Limitation and knowability on possible and rational molecular formulas of natural organic compounds are preliminarily discovered in kinds and quantities based on our researches for years. The delimitate schemes and calculating formulas correspollding to objective realities for the range of molecular formulas below 1000 of molecular weight are tentatively proposed. 203470 molecular formulas which contain only C,H,O,N four elements and molecular weight is from 16 to 800 have been written manually or printed by computer and about 474000 molecular formulas for molecular weight up to 1000 are evaluated. A triangle area which the most of molecular formulas is distributed in it comes out in a coordinate system if the abscissa stands for molecular weight and the ordinate for carbon atomic number in molecular formulas. The triangle,as a head,however,will be a part of whole molecular formula distribution, perhaps as a streamline. Organic chemists will have the initiative in evaluation of experiment data from instruments,calculation of molecular formula according to the delimitate formulas and final determination of them,change the former passive position just accepting experiment data and raise the efficiency of organic molecular structure elucidation if the technique is adopted. The primary foundation for future delimitate and calculation of organic molecular structure will also be laid on the range delimitate and calculation of molecular formulas. Keywords: molecular formula calculation, triangle distribution,application