【Objective】 An in-situ atomic force microscopy (ScanAsyst) was used to study adsorption dynamic and morphological variation of humic acid on the surface of K-bearing biotite. 【Method】 Humic acid is a principal component of humic substances, which are the major organic constituents of soil, peat, coal, eutrophied lakes, and ocean water. Humic acid solutions, the same in pH (6.0), but different in concentration (0 mg L^-1, 100 mg L^-1 and 1 000 mg L^-1) were prepared out of dried humic acid solid. The mineral sheet used in the in-situ observation was biotite, a kind of phyllosilicate mineral belonging in the mica group (2:1 type structure), commonly found in soil. The chemical formula of biotite is K(Mg_2.46Fe_0.45Ti_0.09)[AlSi₃O₁₀](OH) ₂