Aim to simulate the whole fire process of three-story steel frame three-dimensional parking lot structure and study the mechanical properties of the frame structure and components after fire, so as to provide reference for the damage assessment and reinforcement scheme design of such structure after fire. Methods the whole 400 s fire process of the structure was simulated by PyroSim, and the temperature time history curve was obtained. ABAQUS is used to analyze the temperature field of the member section at each time; The structural deformation and internal force of the steel frame parking building under temperature are analyzed by sequential thermal mechanical coupling. Results the temperature of the beam directly above the fire area reached 567 °C, and the temperature of the column reached 100 °C; The temperature distribution of the section is uneven, the temperature distribution of the web and lower flange is higher, and the temperature distribution of the upper flange is lower; The stress in the mid span area of the fire beam and the joint between the fire beam and the main beam is the largest; When the two vehicles are on fire, the deflection of the secondary beam in the middle of span a is 449 mm, exceeding the maximum deflection. The study concludes that the fire resistance of the steel frame is weakest at the mid-span of the fire beam and the joint between the fire beam and the main beam. Post-fire, the mechanical properties of these areas should be thoroughly inspected to develop an effective reinforcement scheme.