Polyaluminum chloride (PAC), microbial flocculant (MBF) and granular activated carbon (GAC) could accelerate the formation of aerobic granular sludge and enhance structural stability. The result of scanning electron microscopy(SEM) showed that the external structure of aerobic granular sludge in control group and MBF group was reticulate and loose, while the PAC group and the GAC group had denser surface structure. And fluorescence in situ staining of extracellular polymers (EPS) showed that the distribution of protein and β-polysaccharide in the main structural components of EPS were the same between the control group and MBF group, which were evenly distributed. The formation mechanism of these two groups consisted to the "EPS hypothesis". PAC-enhanced particles formed a "double-layer structure of protein shell-beta-polysaccharide core". In GAC group, high-density proteins encapsulated granular activated carbon. The formation mechanism of these two groups was more in line with the "crystal nucleus hypothesis". Besides, PAC, MBF and GAC all significantly improved the hydraulic shear resistance of aerobic granular sludge. The capacity of anti-hydrolase resistance was PAC group > GAC group > MBF group > control group.