The chitosan-based intumescent flame retardant (PMC) containing of carbon source, acid source and gas source was synthesized by chitosan (CTS), pentaerythritol phosphate (PEPA)  and diphenyl-methane-diisocyanate (MDI). The structure and thermal stability of PMC were characterized by FTIR, XRD and TG. EP flame retardant coatings were investigated with different flame retardants and three flame retardant coatings (EP1、EP2 and EP3) were obtained. Also these flame retardant coatings were used as protective coatings for steel structure. The thermal properties and flame retardancy of the samples were characterized by TG, Limiting Oxygen Index（LOI）, UL-94 and SEM, the adhesion strength of the coatings were characterized by adhesion experiment. The results showed that the EP3, whose mass fraction of PMC is 10wt%, could meet the standard of UL-94 V-0 rating; the carbon content of EP3 increased by 47% and the LOI of EP3 reached to 25.5% compared with pure EP coating. The results of adhesion experiment showed that the flame retardants will not impair coating’s adhesion strength.