Wind farm simulation is one of the most important processes in wind farm micro-siting.There exists a temperature difference between terrain surface and airflow due to multiple reasons such as sunlight and terrain infrared radiation.When temperature of terrain surface is higher than that of airflow，the temperature difference will cause natural convection and affect the flow near surface.The flow field difference between cases with consideration of this temperature difference and without is studied by running simulation on various terrain types and flow velocities.The simulation uses turbulence model based on standard k-ε model.The result shows that at lower flow velocity on plain terrain，the natural convection caused by temperature difference will affect the simulation result of flow field with a velocity fluctuation up to 10%.At larger flow velocity or on complex terrain，the natural convection still exists but is almost negligible.