Abstract: As a new type of creative composite structure, the research on temperature transfer and temperature field distribution of concrete filled steel tubular with flange connections under fire conditions is relatively weak. Using COMSOL, a numerical model of flange connected concrete filled steel tubular column composite structures is established. Based on this, the deflection changes, stress and strain changes of prestressed bolts, and concrete damage changes of the composite structure under lateral loads before and after fire are studied to analyze the stability of the composite structure. The research results show that the temperature of the outer wall of the steel pipe increases rapidly, and the stress of the bolt under the horizontal load of the component increases significantly after the fire occurs. The stress of the flange at the contact position between the flange and the bolt has a significant redistribution. As the temperature of the component increases, the displacement along the centerline of the bolt gradually increases, and the deflection of the component increases by nearly ten times. Before the fire, with the increase of horizontal load, the damage of components mainly occurs on the back of concrete, but after the fire, the scope of concrete damage has significantly increased. Therefore, under the action of horizontal loads after a fire, the bearing capacity of concrete filled steel tubular structures with flange connections becomes poor.