【Objective】 Humic substances (HS), the main component of soil organic matter, are kind of macromolecular compounds, specific and multi-phased in property, formed during humification. However, in the past two decades, doubts have been arising about rationality of the disassociation process of HS. Currently, the research has shifted its focus from on chemical properties of HS to on identification of processes and mechanisms related to HS renewal and stabilization. Plant residues and microbial biomass are the main parent materials for the formation of humic substances, meanwhile, clay minerals, as an important part of the soil, also play an important role in the process. However, still little is known about any specific effects of clay minerals on formation of HS. Some scholars have used microbial pure culture methods to study formation of HS, but because of the absence of clay minerals, the formation of HS studied does not represent that in soil. Therefore, more efforts should be done to further elucidate in detail the complex interactions between HS and the surface of minerals, as well as the role of soil microbes as a participant. In order to explore effects of montmorillonite on humification process, white alfalfa, an angiosperm, was used in an incubation experiment with montmorillonite and microbe-soil extract as control conditions. 【Method】 In this experiment, there were three treatments, i.e. Treatment A, white alfalfa with montmorillonite and soil extract added; Treatment AnM, white alfalfa with soil extract added only; and Treatment AnI, only white alfalfa. Effects of the treatments and duration of the incuabtion on composition of humus-like substances and structure of humic-like acids（HLA）formed as incubation product of white alfalfa were studied. Water-soluble substances（WSS）, fulvic-like acid（FLA）, humic-like acid（HLA） and humin-like（HLu）were extracted with the modified humus composition method. HLA samples were extracted with the method recommended by the International Humic Substances Society (IHSS) for analysis of structure of HA with the elemental composition- infrared spectroscopy. 【Result】 Results show that the amendment of montmorillonite promoted decomposition of TOC and accumulation of simple structured HLA. After 90 days of incubation, H/C in Treatment A increased from 1.38 to 1.61, after 180 days from 1.39 to 1.53, and after 360 days from 1.36 to 1.48. The sharp increase in H/C in the early stage in Treatment A made the structure of HLA simple. However, with the incubation going on, the increase in H/C gradually dulled in trend. Its ratio of 2920/1640 in the infrared spectrum tended to be in consistence with that in elemental composition. At the end of the incubation, HLA, regardless of treatments, developed eventually quite close to the O/C and H/C of soil HA in value. Among the treatments, the HLA in Treatment (AnM) was the closest to real soil HA in complexity, indicating that montmorillonite cannot help HLA turn into soil HA. 【Conclusion】 Overall, montmorillonite amendment may promote decomposition of TOC and formation of HLA, and accelerate humification process of white alfalfa; however, it does not enhance the aromatization of HLA in degree and the structure of HLA in complexity as speculated or reported in the literature. Instead, it simplifies the structure of HLA, which is still quite different from real soil HA.