Abstract: This paper cares about the relationship about the block variables instead of individual topological index so that we can use subspace comparison to study the high dimensional problem. The data are about five series of topological indices of 530 saturated hydrocarbons. By the cosines of the angles between any two block-variables, the linear correlation between different block variables is studied. It is a good model of boiling point of 530 saturated hydrocarbons with variables, which are selected by the subspace comparison. The subspace comparison is a new method to select variable.

Key words: Subspace comparison, Topological index, Block variable, Variable selection