The invention discloses a method for preventing and controlling 
nitrogen and 
phosphorus non-
point source pollution in farmland. The method comprises the steps of control over a source of the farmlandnon-
point source pollution, wherein the use amount of chemical 
fertilizer and chemical 
pesticide is reduced; 2, adoption of a farmland 
ditch interception 
system, wherein multiple longitudinal ditchesare excavated at equal intervals in the width direction of the farmland, multiple transverse ditches are excavated at equal intervals between every two adjacent longitudinal ditches, and bio-carbon 
layers, soil 
layers, bio-carbon 
layers and soil layers are sequentially laid in the longitudinal ditches and the transverse ditches respectively from top to bottom; 3, adoption of a farmland 
tail waterpurification interception 
system, wherein a 
water collection ditch communicated with the longitudinal ditches is formed in the 
ridge of the farmland, and a water purification device is arranged belowthe lower end of the 
water collection ditch and comprises a water collecting and sand setting tank, a 
hydrolysis acidification tank, an anaerobic 
sedimentation tank, an ecological purification tank and a clear 
water pool which are communicated with one another in sequence. According to the method, not only can 
residual nitrogen and 
phosphorus elements in the farmland be efficiently and quickly removed, but also 
discharge of 
nitrogen and 
phosphorus can be effectively controlled, and recycling of farmland drainage is achieved.