Abstract: In order to study the temperature development characteristics and structural response of the portal frame under different fire scenarios, four localized fire tests and one destructive spreading fire test were carried out on a reduced scale portal frame structure model. The heat release rate (HRR), ambient temperature, steel component temperature and structural displacement were measured. The test results show that the temperature rise characteristics of the structure under small fires are different from those of the large spreading fire. The localized small fires demonstrate fuel-controlled combustion, and the upper gas temperatures are higher than those at lower locations. In the large fire test, the gas temperatures at lower locations are higher than the upper ones due to insufficient combustion. For structural components, the temperature rise of the beams and columns near the fire source lags behind the ambient air. In the large fire test, considering the spreading nature of the fire, the temperature changes around the fire site are more complex. The temperature rises and displacement changes of the structural components at different positions demonstrate corresponding time sequences. Despite the 2 h fire protection of the steel columns according to relevant fire standards, the failure of the steel beam led to the overall inward collapse of the portal rigid frame in 32 mins. It can be seen that, for the portal frame structures with weak structural redundancy, members with small fire resistance limit impose great impact on the fire resistance of the whole structure, and it is recommended that structural fire safety design should be considered in perspective of the overall fire resistance performance of the structure.