The invention discloses modified montmorillonite as well as a preparation method and application thereof. The preparation method of the modified montmorillonite comprises the following steps of: putting calcium-based (sodium-based) montmorillonite into a magnetic crucible and calcining for 8 to 24 hours at constant temperature of 600+/-10 DEG C in a muffle furnace; and then, taking out when the furnace temperature is lowered to 105 DEG C, and preserving in a dryer for later use. When the modified montmorillonite obtained by preparation is used for adsorbing an organic pollutant, the adsorption effect is good. The invention has simple preparation steps and low requirement to operation technique, and the adopted original montmorillonite is a commodity, can be directly purchased and has cheap price.