Wind speed turbulence intensity is crucial for wind turbine structure design and aerodynamic loads calculation. In the study, the actual turbulence intensity observations are compared with the Normal Turbulence Model defined by IEC standard. The results show that the Normal Turbulence Model overestimates the turbulence intensity. A new turbulence intensity model is proposed based on the actual observations, which shows better performance than the Normal Turbulence Model. Then the variation pattern of turbulence intensity during a day is analyzed. The turbulence intensity exhibits obvious daily periodicity in two wind farms. Furthermore, the causes of daily periodicity are discussed and verified by the wind speed dataset 3. Finally, an improved time-varying turbulence intensity model is developed according to the daily periodicity. (C) 2018 Elsevier Ltd. All rights reserved.