The influence of sepiolite on the properties of water-based steel structure fire retardant coating was studied.The experimental results show that the intumescent state,fire retardant property and water resistance of the coating are improved by the addition of proper content of sepiolite.Furthermore,viscosity and water resistance of the coating and hardness of the char layers increase with the increase of content of sepiolite,but intumescent ability is reduced.The optimum content of sepiolite in the coating is 2.88%(mass fraction) by colligating various factors.