The combination of silicone emulsion and self-crosslinking polyacrylate emulsion was used as a binder for preparing a kind of water-borne ultra thin intumescent fire retardant coating for steel structure.The influence of the binder on the properties of fire retardant coatings was investigated.The experimental results show that the state of charring layer,fire retardant properties and intumescent rate of the coatings are improved by the addition of proper content of silicone emulsion.The coating has the superior properties when the content of silicone emulsion in the binder is 32.9%(by mass) and the content of binder was 16.7 %(by mass).