In order to investigate the fire resistance of high strength steel beams made from Q460, the method to compute temperature distribution of high strength Q460 steel beams was derived and the temperature distribution was calculated by using finite difference method. The modified equations of temperature for components of steel beam were proposed. According to critical moment at room temperature and mechanical properties of high strength Q460 steel at elevated temperature, the critical moment and stability checking coefficient were obtained by analysis. The load bearing capacity and critical temperature as well as stability factor were studied by using equivalent stiffness method through considering the effect of temperature gradient on stiffness.