In this study, Humic acids from soils with different fertilization were fractionated into seven fractions by alcohol precipitation technique, and the fractions absorption by Ca²⁺ saturated monhnorillonite was studied. The results showed that the absorption could be described by single surface Langmuir, double surface Langmuir and Freundlich equations. The change trends of absorption amount and strength were not consistent with the fractions number order. Of all the seven factions, fraction 4 or 3 had the largest absorption amount and strength, suggesting that fraction 4 or 3 was the optimum absortion fraction which had the optimum molecular state for absorption. Compared with no fertilizer and chemical fertilizer, the absorption amount and strength of the optimum absorption fraction of organic materials increased.