Because the flame retardant viscose fibers used in textiles of a company have better flame retardant effect than those of common flame retardant cellulose fibers sold in the market, and the flame retardant properties do not be decreased after dyeing, finishing and washing many times. it is of great significance to study the structure and morphology of the flame retardant viscose fibers for the market application of textiles. The flame retardant viscose fibers and flame retardant cellulose fibers were analyzed by X-ray fluorescence spectroscopy. The main components, structure and adding methods of two flame retardant cellulose fibers were defined, which can be used to infer the flame retardant mechanism and application direction of the fibers.