In order to improve the grafting modification degree and flame retardant effect of adenosine phosphate monomer on cotton fabric, glycyl methacrylate (GMA) was used to modify adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP), obtaining three kinds of flame retardant monomers of AMP-m-GMA, ADP-m-GMA and ATP-m-GMA with unsaturated double bond. Subsequently, three flame retardant monomers were grafted onto cotton fabric via UV photografting to prepare photografted flame retardant cotton fabrics with AMP-m-GMA, ADP-m-GMA and ATP-m-GMA, respectively. The structure characterization and thermal stability analysis of three flame retardant monomers were carried out, and the thermal stability, flame retardant performance, combustion behavior and structure of residual carbon of three photografted flame retardant cotton fabrics were investigated. The results showed that unsaturated double bonds were introduced onto three adenosine phosphate monomers with good thermal stability through ring-opening reaction of epoxy group of GMA. Compared with pristine cotton fabric, the maximum thermal degradation rate of three kinds of flame-retardant cotton fabrics decreased by 60.0%, 52.0% and 60.0%, the limit oxygen index increased from 16.1% to 25.39%, 27.38% and 26.38%, and the heat release rate of the fabrics decreased by 15.09%, 60.47%, 37.82%, respectively. These results implied that three flame retardant adenosine phosphate monomers could help cotton fabric form dense carbon layer, prevent heat diffusion, and obtain good flame retardant effect. Among three photografted flame retardant cotton fabrics, the weight gain rate of ADP-m-GMA flame retardant cotton fabric could reach 22.4% and the damage length after burning was reduced from 30 cm to 14.2 cm, demonstrating better flame retardancy.