Observation data show that natural wind has a characteristic of regular time-variation in speed and direction. However, the time-varying inflow conditions are usually simplified as a constant wind profile in simulations on airflow and pollutant dispersion in urban street canyons and/or building cluster. The study on characteristics of urban canopy layer (UCL) flow under time-varying inflow conditions should be further contribute to the understanding of pollutant and energy transport processes in the urban atmospheric environment. In the current work, typical studies on air flow and pollutant dispersion in urban street canyons and building array are reviewed. The time-varying upstream inflows could commonly enhance the transportation of pollutant and energy in actual UCL. Studies have revealed that the variation of natural inflow conditions could be one of the primary factors that influencing the transport efficiency of pollutant in urban street canyons. Perspectives on methods in performing the time-varying inflow conditions are provided as well. Gradual and/or stepped variation of wind data would be expected in numerical simulations.