Abstract: The harmonic synthesis method is used to simulate the time history of turbulent wind in a land wind field with Davenport and Kaimal wind speed spectrum. According to the average wind velocity at the corresponding height and combined with Bernoulli theory, the wind load time history is obtained. The finite element model of a 3 MW wind turbine steel tower is established by considering the aerodynamic thrust, wind load time history and second-order effects of gravity. The dynamic response of the steel tower is also solved. Taking the variations of both load effect history and material density into account, the Monte Carlo method is used to analyze the failure probability of foundation slab void according to the criterion in the code, and the corresponding variation laws of reliability index with different radii of foundation slab are discussed. The results show that: the total bending moment and total shear force at the bottom of the wind turbine tower are approximately perfect dependent of each other and have a large coefficient of variation, regardless of normal operating conditions or extreme load conditions; for the selected Davenport wind speed spectrum, the failure probability of the foundation slab void of the wind turbine is about 0.008 20 and 0.0188 under normal operation and extreme load conditions, respectively, and for the selected Kaimal wind speed spectrum, the corresponding failure probability is about 0.0107和0.0281, respectively; the reliability index increases with the increase of the radius of foundation slab, by no less than 39.90% for both two working conditions when the radius increases to 1.2 times.