This paper has studied the structure and flame-retardant properties of flame-retardant cellulose fiber with DDPSN as flame retardant. The flame retardants was uniformly dispersed in the cellulose /[Amim]Cl Solution to obtain the good spinnable dope, then the dope was wet-spun. Effects of the flame-retardant contention the fiber structure and properties were investigated. The surface of the flame-retardant cellulose fiber was observed using field emission scanning electron microscope (FESEM). Besides, through the Simultaneous thermal analysis, it has been shown that, with the increase of fame retardant, the degree of fame resistance was obviously improved. The flame retardant acted greatly in condensed phase during the fiber degradation and remained mainly in residues after degradation, the experiments show that the flame-retardant properties of flame-retardant cellulose fiber with 20wt% DDPSN was obvious.