To investigate the mechanical behavior of reinforced concrete structure subjected to fire, the incremental thermoelasticplastic creep constitutive equations of steel and concrete in consideration of temperature and creep deformation were obtained based on different yield rules and the elasticplastic theories. The nonlinear analysis for reinforced concrete simply supported slab was carried out with consideration the variation of the mechanical properties of steel and concrete with temperature. The effectiveness and applicability of the constitutive equations were verified with the test results from relevant literature. The nonlinear analysis was employed for onebay onestorey reinforced concrete frame under fire and the variation of displacement at partial nodes was analysed. It was found that the reinforced concrete structure at a high temperature would have a significant deformation. And the displacement change curves of beamcolumn joints of reinforced concrete frame were not monotonous trend and there were inflexion points. The vertical displacement values of beamcolumn joints were less than those at midspan of crossbeam.