Abstract: In order to study the flow field characteristics of large horizontal axis wind turbine under wind shear, the NH 1500 kW large horizontal axis wind turbine was taken as the research object. The flow field characteristics such as instantaneous velocity component, pulsation velocity and wind turbine output power were analyzed by IDDES (improved delayed detached eddy simulation) method with high simulated flow field accuracy in CFD . The results show that the flow field velocity around the wind wheel plane fluctuates greatly, and the axial velocity increases outside the rotating boundary of the wind wheel, while decreases within the rotation boundary. The spectral characteristics of the pulsation velocity are related to the integer times of the rotation frequency of the wind wheel in the low frequency region. The simulated wind turbine power in cosine form satisfies the turbulent spectral characteristics.