This paper investigates the parameter evaluation of mechanical behavior of high strength structural steels in fire-resistance design. In order to reveal the elevated-temperature mechanical properties of high strength steel S460N, tensile tests were conducted under both fire conditions of steady state and transient state. The elevated-temperature reduction factors of elastic modulus, yield and ultimate strengths of S460N were obtained and compared to those in the current design standards and available literature. According to the comparison between the research results on S460N, the available research results in literature on S460N, S460M, Q460 and various mild steels, it is found that the deterioration of mechanical properties of structural steels at elevated temperatures is dependent on steel grades and manufacturing method. Therefore, the recommendations in current design standards are not applicable to high strength structural steels. Moreover, unique predictive equations for the deterioration of S460 mechanical properties at elevated temperatures were proposed and validated against the available literatures.