Abstract: The synergistic effects on flame retardancy and smoke suppression of the cotton fabric flame retarded with cyclic phosphonate ester MCPPE were discussed in this paper. The results showed that the LOI of flame retardant cotton with MCPPE increased from 43% to 52% as adding 0.4 g/L bismuth oxide in MCPPE flame retardant finishing agent. Damaged carbon length shortened to 5cm, vertical flame reached B1 level and for breaking strength the influence was not strong. Thermogravimetric analysis showed that bismuth oxide further reduced the initial decomposition temperature and maximum pyrolysis temperature. SEM showed the char of the burned cotton was denser after adding bismuth oxide and bismuth oxide had obvious resistance to deformation capacity. Cone test showed that bismuth oxide not only reduced the total heat release rate of flame retardant cotton fabrics but lowered total smoke yield 60%.