Influence of rheological additives on the performance of intumescent fire retardant coatings was investigated by using solvent-based acrylic resin and chlorinated paraffin as binder, APP, PER, and MEL as the intumescent system. The influence was analyzed according to char residual mass, fire resistance time, char expansion, char strength and morphology.The results showed that different types of rheological additives had remarkableeffect on the performance of intumescent fire retardant coatings. Polyamide wax and hydratedmagnesium silicate almost had no impact on the char strength，relative char expansion and fireresistance. Modified hydrated magnesium silicate could improve the char strength and fireresistance time. Hydrophilic fumed silica could increase the relative char expansion and fireresistance time，but at the same time，it could reduce the char strength and cause it to peel off easily.Hydrophobic fumed silica and modified montmorillonite rheology additives could inhibit swelling and foaming and improve the char strength，but at the same time，they would significantly reduce the fire resistance time. Finally，the mechanism of rheological additives on the performance ofintumescent fire retardant coatings for steel structure was analyzed. The main mechanism ofrheological additives on the performance of intumescent fire retardant coatings was attributedto the impact of the high temperature viscoelastic properties and char expansion.