The use of pesticide such as azinphos-methyl (AZPM) is rapidly increasing around the world, which has posed critical effects on humans and home environment. In the present study, azinphos-methyl was employed as a model to explore the photocatalysis effect of various cation-modified montmorillonite in the soil under visible-light irradiation. For six types of cation-modified montmorillonite(M), the photodegradation rates of AZPM follow the order: Fe3+ >Al3+ >Mg2+ >Ca2+ >K+ >Na+, which is similar to the photo-Fenton-like degradation. To further study the effect of clay type, four types of clays were paralleled, and Fe(III)-montmorilloniteodified smectite shows the highest photodegradation rate followed by Al(III)-modified smectite, suggesting that Fe3+ content plays a key role in photocatalysis degradation of AZPM. Moreover, O,O,S-trimethyl phosphorodithioate and methyl 2-aminobenzoate were determined by GC-MS analyses as the main intermediate compounds, which was degraded into small molecular products, and speculated the catalytic mechanism of AZPM at Fe(III)-montmorillonite surface. In addition, center dot OH (free radical) that measured by electron paramagnetic resonance is formed on Fe(III)-montmorillonite under light with H2O, and it accelerates the photodegradation process of AZPM.