The invention discloses an in-situ treatment method for farmland recession, belongs to the field of ecology and environment protection and in particular relates to a method for removing nitrogen, phosphorus and organic matters from farmland recession by using a multilayer immobilized material of periphyton adhesion composite flora. The method comprises the following steps: performing culture and domestication on ordinary anaerobic granular activated sludge and aerobiotic activated sludge so as to obtain anaerobic ammonia oxidation granular sludge and aerobiotic nitration granular sludge, performing separation screening and activity retention drying so as to obtain the kernel of the multilayer immobilized material of composite flora, and performing pelletizing by using a sphere molding mold, so as to obtain the multilayer immobilized material of the composite flora. The multilayer immobilized material of the composite flora is applied to a recession bank of a farmland, periphyton adhesion growth on the recession bank is achieved, natural seepage of farmland recession passes through the recession bank with sufficient sunshine, and a periphyton intensified denitrification system for farmland recession pollution prevention and control can be constructed. By virtue of the characteristics that an immobilization microorganism technique is high in biological concentration and good in environmental adaptability, successful application of the immobilization microorganism technique in rural water environment control can be achieved.