Abstract:The structure and properties of the charring layer of the intumescent fire-retardant coating for structure steel was studied and four parameters model, including(1) thickness of the charring layer,(2) strength of the charring layer,(3) surface status of the charring layer,(4) quantitative analysis of the charring layer's inner bubble structure, for the evaluation of the charring layer of the intumescent fire-retardant coating was established.Meanwhile, feasible measurements for these parameters are presented and the relations between the fireproof performance and the change of these parameters are also discussed through experimental data analysis.