Reinforced　concrete　(RC)　columns,　as　a　main　vertical　load-bearing　structural　component,　may　be　seriously　damaged　in　the　event　of　fire　and　explosion　accidents,　thereby　affecting　the　safety　of　the　building.　In　the　current　work,　the　lateral　impact　resistance　of　RC　columns　under　two　fire　scenarios　(at　high　temperature　or　after　cooling　from　high　temperature)　is　discussed　using　a　3D　mesoscopic　model.　In　the　modeling　process,　the　heterogeneity　of　concrete　and　the　bond-slip　behavior　between　longitudinal　reinforcement　and　concrete　were　taken　into　account.　In　addition,　the　differences　in　impact　resistance　of　RC　columns　at　high　temperature　and　after　cooling　with　different　fire　durations　were　analyzed,　and　some　quantitative　conclusions　were　given.　The　results　show　that　the　mesoscopic　numerical　model　considering　the　relative　slip　of　steel　bar　and　concrete　can　reasonably　reflect　the　mechanical　response　of　the　RC　column　under　impact　load　or　fire.　Exposure　to　the　same　fire　duration,　the　impact　resistance　of　the　RC　column　at　high　temperature　is　weaker　than　that　after　cooling　due　to　the　severe　deterioration　of　material　mechanical　properties　at　high　temperature.　The　damaged　area　and　the　maximum　plastic　strain　of　the　column　increased　as　the　fire　duration　increased.　The　mid-span　peak　and　residual　deflection　of　columns　increase　linearly　with　the　increase　of　fire　duration.　Under　the　same　fire　scenario,　the　peak　and　residual　impact　force　of　the　column　increases　nonlinearly　with　the　fire　duration,　while　the　peak　reaction　force　decreases　linearly.　The　fire　scene　has　little　effect　on　the　axial　force,　shear　force　and　bending　moment　of　the　RC　column　under　the　same　fire　duration.　In　addition,　the　mechanical　behavior　of　the　column　ends　and　mid-span　areas　need　to　be　considered　in　the　design　due　to　their　obvious　changes　in　internal　forces.