The bottom of wind turbine foundation will cause fatigue damage under wind loads. In order to study the fatigue reliability of wind turbines under wind loads, the random fluctuating wind loads were expanded orthogonally, and the expanded wind load model was used to calculate the fatigue reliability of the wind turbine tower using the number theory selection method and the probability density evolution method. The thrust coefficient method was used to calculate the stress time history of the dangerous part of the wind turbine foundation under the wind load, and then the fatigue damage of the point was calculated by the rain flow counting method, which is substituted into the probability density evolution equation. The probability density function of fatigue damage can be obtained by solving differential equation. By accumulating the probability of fatigue damage less than 1, the fatigue reliability of the dangerous parts can be obtained, that is, the fatigue reliability of the entire foundation. The effectiveness of the proposed method is verified by a 3 MW wind turbine. Using the probability density evolution method, the fatigue reliability of the foundation under wind load can be accurately given. The findings of this paper have reference significance for the calculation of fatigue reliability of wind turbine foundation under similar working conditions.