Abstract: Microalgae is a unicellular photosynthetic organism with the characteristics of high photosynthetic efficiency, strong environmental adaptability and short growth cycle. Microalgae polysaccharides are natural macromolecular substances widely existing in microalgae. They can not only promote crop growth, improve crop resistance, but also improve soil physicochemical properties, regulate soil microbial communities. They are also a potential source of plant bio-stimulants. However, microalgae polysaccharides have not been widely used and developed in agriculture. In this paper, the biosynthesis pathway, biochemical composition, growth-promoting and anti-stress mechanism of microalgae polysaccharides and their effects on soil improvement were reviewed. The aim is to provide a scientific and theoretical basis for large-scale preparation and agricultural application of microalgae polysaccharides.