In order to study the effect and mechanism of extracellular polysaccharides on the stability of anammox granular sludge, amylase which can enzymolyze polysaccharides was used to enzymatically hydrolyze granular sludge. The results showed that the outer edge of the granular sludge in the α-amylase treatment group swelled, while the surface of the granular sludge in the β-amylase treatment group did not change significantly, but it was broken and the stability was obviously reduced. The surface properties and XDLVO theoretical analysis show that enzymatic hydrolysis reduces the hydrophobicity of granular sludge and increases the repulsive force between microorganisms, thereby affecting the stability of granular sludge. The results of Fourier infrared spectroscopy showed that the content of hydrophobic functional groups in extracellular polymers of sludge was significantly reduced after enzymatic hydrolysis. Confocal scanning found that the content of α-D-glucopyranose polysaccharide at the outer edge of the granular sludge in the α-amylase treatment group was significantly decreased, while the β-D-glucopyranose polysaccharide in the β-amylase treatment group was distributed in fragments. Therefore, the α-amylase treatment group showed that the hydrophobic effect of extracellular polysaccharides, binding to each other through O-H functional groups or bridging with cations can promote the aggregation between microorganisms. The β-amylase treatment group showed that the entanglement between the long backbones of extracellular polysaccharides and the bridging of abundant binding sites to form a skeleton enhanced the adhesion between microorganisms and was beneficial to the stability of granular sludge. The research results of the thesis provide a new understanding of the stability of granular sludge from the perspective of extracellular polysaccharides.