The epoxy-based intumescent fireproof coatings for steel structure were prepared with organic montmorillonite（OMMT）and nickel chloride（NiCl₂）as the compound synergists，and the fireproofing and smoke suppression effects of the compounding synergists in the fireproof coatings were systematically investigated by means of cone calorimeter，thermogravimetric analysis（TG）， scanning electron microscopy（SEM）and Fourier transform infrared spectroscopy（FT-IR）. The results showed that adding OMMT or NiCl₂ alone could effectively enhance the thermal insulation performance of the epoxy-based intumescentfireproof coatings for steel structure and reduce the heat release and smoke production duringthe combustion process，and the use of the two in combination showed a better synergisticeffect. When the mass ratio of OMMT and NiCl₂ was 1∶1，the backside temperature of the coated steel was 300 ℃ at 1 465 s，and the peak heat release rate and peak smoke production rate were down to 291. 3 kW/m² and 0. 039 m²/s，respectively. In addition，TG results showed that the mixture of OMMT and NiCl₂ could reduce the peak decomposition temperature and mass loss rate of the coatings，resulting in the residual carbon rate was up to 24. 8% at 700 ℃.SEM and FT-IR revealed that the combination of OMMT and NiCl₂ was conducive to the formation of more phosphorus-containing compounds to improve the densification and continuity of the expanded charcoal layer to achieve a better fire and smoke suppression effect.