Abstract: The structure-activity of amine collectors, N-dodecyl-1,3-diaminopropanes (DN₃) and N-lauryl ethylenediamine (DN₂), was studied systematically with formulas derived by the authors. It is concluded that the collectors are characteristic of the smaller group electronegativity, the smaller absolute value of energy level difference of frontier molecular orbitals, the larger polar group diameter and the higher center atomic net charge. The collectors were used in reverse flotation of hematite for desilicication. The results show that the selectivity and collecting performance of DN₃ and DN₂ are better than those of dodecylamine (CH₃(CH₂)₁₁NH₂). The selectivity of DN₃ is better than that of DN₂, while the collecting performance of DN₂ is better than that of DN₃. These calculation results are in accordance with the flotation test ones.