Due to the lower ash formation temperature of circulating fluidized bed fly ash (CFB-FA),  its amorphous fractions are significantly different from conventional  pulverized coal furnace fly ash (PC-FA). At present, the chemical composition and structure of the amorphous components in CFB-FA are not well understood. Taking four kinds of CFB fly ash as the research object, the Retiveld full spectrum fitting method and the acid-alkali-based alternate method were used to calculate the content of amorphous components in fly ash.Combining the chemical composition and mineral quantitative results, the main chemical composition of the amorphous components in the CFB-FA was obtained. Based on the 27Al and 29Si magic-angle rotating nuclear magnetic resonance (NMR) spectrum, the coordination structure of silicon and aluminum in the amorphous component was revealed using the rewind integral peak fitting method. The results show that the main phase of the four CFB ashes is amorphous aluminosilicate, the mass fraction of which is more than 65%, and the main chemical compositions of amorphous components are SiO2 and Al2O3. The Si/Al (molar ratio) of amorphous component is lower than the total Si/Al of the raw fly ash. The contents of amorphous components in the CFB-FA obtained by acid-alkali alternate method are slightly lower than those calculated by Retiveld full spectrum fitting. NMR results reveal that the Si-O-Si and Si-O-Al structures of amorphous components in the CFB-FA are highly disordered and unstable. The aluminum in the amorphous component of CFB-FA ash mainly exists in four-coordinated (［AlO4］) and six-coordinated (［AlO6］) aluminum oxide structures. The silicon in the amorphous component is mainly Q4 (0Al) structure. ［SiO4］ structures are connected by bridging oxygen to form Si-O-Si structure with high degree of polymerization; and ［AlO4］or ［AlO6］ combines with ［SiO4］ to form Si-O-Al structures of Q3 (1Al) or Q4(1～2Al). The HCl solution destroys ［AlO4］ structure and causes Al to dissolve, and the NaOH solution destroys ［SiO4］ structure and causes Si to dissolve. The Si and Al in amorphous composition of CFB ash can be separated by the acid-alkali-based alternate method.