To investigate the fire development，smoke movement，and temperature development within the whole building and steel members，a 1 ∶ 4 scaled portal frame building was designed and built for a medium fire test. The temperatures of the hot gas and steel members were measured in the test. The formulation recommended by《Code for fire safety of steel structure in buildings》(GB51249-2017) was used to predict the temperature-time curves of steel members. The test results indicate that the maximum temperature of hot smoke decreases from the fire origin to the surrounding zone and distributes symmetrically on either side of the roof ridge. In the case of localized fire，the space in the building can be divided into high temperature zone of hot smoke layer，sub-high temperature zone and zone below the hot smoke layer. The temperature distributions within the steel sections are approximately uniform. The temperature variation of steel members lags behind that of the surrounding hot gas during the growth and decline stage. Meanwhile，the effect of flame radiation on the temperature elevation of steel members under the hot smoke zone needs to be considered in addition.