Abstract: Based on the standard test method, the steady-state tensile coupon testing on SQ410FRW fire-resistant weathering cold rolled steel strips for floor decking system manufactured by Shougang Group, was carried out in order to investigate their characteristic mechanical properties at elevated temperatures. These properties mainly include high-temperature modulus of elasticity, proof strength at specified plastic strain, tensile strength, percentage elongation after fracture and percentage reduction of cross section. The corresponding expressions for the reduction factors were obtained by nonlinear regression method, so as to represent the high-temperature mechanical performance indicators. The stress-strain constitutive model was further established by adopting Ramberg-Osgood model for the experimental stress-strain relation curve. The model will be applied in the subsequent finite element parametric modelling, aiming at the thermal analysis and sequentially coupled thermal stress analysis of structural members. The following conclusions are drawn from the test results: Most tensile specimens show fracture within the gauge length, and the percentage elongation after fracture increases with temperature rising. The high-temperature modulus of elasticity, proof strength at specified plastic strain and tensile strength drop slowly under 600℃, and still maintain over 60% of nominal values at room temperature, basically meeting the requirements of the properties of fire-resistant steel. The fitting goodness of stress-strain constitutive model all exceeds 90%, showing good agreement with the experimental stress-strain curves. Therefore, the proposed constitutive model can be applied in the finite element analysis of the fire resistance of relevant structural members.