The invention discloses a method for preparing a montmorillonite forming adsorbent. The method comprises the following steps of: 1, taking powdery sodium-based montmorillonite; 2, adding a forming agent into the powdery sodium-based montmorillonite, stirring the mixture to form micelle, and putting the micelle into a forming machine and pressing the micelle into glue strips; 3, ageing; 4, drying;and 5, roasting, crushing and screening. The method for preparing the powdery sodium-based montmorillonite into the montmorillonite forming adsorbent does not change good adsorption performance of the montmorillonite, scientifically and effectively utilizes the effective ingredients and physicochemical properties of the montmorillonite, reduces the swelling property of the montmorillonite and reduces adverse effect of wastewater treatment subsequent processes.