Field measurement of wind turbulent properties is a long-term and fundamental task for structural wind engineering since uncertainties of wind load is actually the key factor that affects the analysis accuracy of wind-resistant structures.Among many turbulent wind parameters as wind spectrum

wind profile

turbulent intensity and so on

the joint probability density function of mean wind speed and direction is an important but less addressed property.This paper presents an empirical joint probability density function（JPDF）of mean wind speed and direction.The proposed JPDF model is actually built from marginal distributions of wind speed and wind direction which are assumed as an Extreme-Value distribution.The model has seven unknown coefficients that can be obtained by fitting the model to the field measured data.Details of the JPDF model are first discussed with focus on modeling procedure for both unimodal and bimodal scenario and approaches for determining the modal parameters.The applicability and feasibility of the model is then validated by three different types of field measurements

which are unimodal and bimodal wind data from parent population and bimodal wind sample form extreme value data.It is concluded from the results that the proposed JPDF model can represent quite well the joint distribution properties of wind speed and direction from different data source

and it can be further adopted for determining the directional design wind speed and assessment of wind energy.