The invention discloses a saline and alkaline land improvement method. The improvement method comprises the following steps: crushing plant straw to prepare plant straw powder, then, scattering the plant straw powder into saline and alkaline land, and carrying deep ploughing and turning; applying a mixture consisting of soybean meal, furfural residues, activated biochar powder, a microbial agent,inorganic fertilizer, natural zeolite powder, mineral-sourced humic acid and modified calcium alginate aerogel to the surface layer of the saline and alkaline land, and using a rotary cultivator for rotary cultivation and mixing; flattening the soil surface layer of the saline and alkaline land, uniformly sowing alfalfa seeds on the flattened saline and alkaline land, then, performing earthing up,and controlling the sowing depth at 1-2 cm; during harvesting, keeping the stubble height of alfalfa at 5.5-7.5 cm; carrying out deep ploughing, turning and burying on the saline and alkaline land toturn and bury the alfalfa stubbles in the soil; and then, planting wheat or corn crops. The method can effectively reduce the soil alkalization degree and salt content, and the physiochemical properties of the soil are effectively improved.