Abstract 【Objective】The sorption of pesticides (including herbicides) by soil is an important factor affecting environmental behaviors of the substances. It is important to investigate effects of composition manner and complexation degree of the organic and inorganic components in particles different in size on pesticide sorption-desorption behaviors in the soil, and their contributions to pesticides sorption in the soil. 【Method】In the current study, soil samples of 7 different types of soils were collected from six different provinces or regions and processed physically and separately for extraction of three particle-size fractions, that is, clay (﹤0.002 mm), silt (0.02～0.002 mm), and sand (0.05～0.02 mm), of organo-inorganic compounds. The batch equilibrium method was used to explore rule for allocation of butachlor in the interfaces between different particle-sized compounds and soil solution and at the same time quantitative calculation was done of contributions of the different particle size fractions of compounds to the total butachlor adsorption in the soil. In the end, analysis was performed of butachlor adsorption characteristics of total organic carbon (TOC) in different particle size fractions from the angle of organo-inorganic compounds.【Result】 Results show that the clay fraction was the highest in butachlor adsorption capacity but the lowest in desorption rate, while the sand fraction was the lowest in adsorption capacity but the highest in desorption rate. The contribution rate of the three fractions to butachlor adsorption ranged from 36.7 to 72.4%, from 21.7 to 50.5 % and < 10 % for clay, silt and sand fractions, respectively. TOC was the key factor affecting butachlor sorption in the three fractions of the soil, but how much was the effect depends on physico-chemical properties of the TOC per se in each fraction and degree of the TOC compounding inorganic minerals. In the clay fraction, butachlor retention on TOC was affected significantly by inorganic minerals; in the silt fraction, it was not much affected; while in the sand fraction, it was almost not affected. 【Conclusion】In the current study, bioavailability of butachlor absorbed in different soil size fractions and migration of the substance in the environment was effectively predicted. The findings can be used to serve as theoretical basis for farmers to rationalize application of butachlar in the light of soil type so as to reduce environmental pollution.