3-D unsteady mathematical model of natural ventilation condition in Venlo type greenhouse was built up by CFD method. The boundary conditions were based on solar radiation, external air temperature, wind velocity and direction changing over time. The result shows that the inside temperature change had the same variation tendency with the outside temperature change during the whole simulation period. The mean temperature difference of the indoor and outdoor temperature was 3.09℃. RMSE of the simulated and measured value was 0.688℃. The maximum relative error and the average relative error was 8.9% and 2.8%, respectively. The CFD-based model could accurately represent the temporal and spatial variation of indoor temperature. When the outside wind speed changed from 0.81m/s to 1.2m/s and the wind direction changed from south southwest to west, the local airspeed near the west windward entrance firstly increased and then decreased. The airflow speed in the east area was markedly increased. The average temperature of x=1.5m cross section at the entrance of ventilation and crop canopy dropped 1.87℃ and 0.92℃ in 180s. Cooling effect of natural ventilation was remarkably affected by wind speed and direction.