To study the indoor environment parameters dynamic response to the instantaneous variation of outdoor meteorological conditions in Lanzhou，a standard k-ε turbulent model of CFD is adopted to numerically analyze the pollutant concentration field and airflow distribution in an office when the unsteady heat transfer through outer walls is considered.The velocity field，temperature field and pollutant concentration field of two air supply modes，ceiling air supply and lateral air supply，are obtained.The results indicate that the pollutant concentration field and migration characteristics are affected significantly by the solar radiation resulting from stimulating the natural convention heat transfer in the room.Under the same air supply mode，the indoor pollutant concentration is more uniform at 16:00 than that at 8:00.And the average value of pollutant concentration at 8:00 is relatively higher than that at 16:00.At the same air supply parameters，the ceiling air supply mode is more beneficial to lower the indoor pollutant concentration.