In order to accurately and efficiently evaluate the mechanical properties of semi-rigid joints in transmission towers, a method based on surrogate model is proposed to predict the moment-rotation relationship of the semi-rigid joints. By introducing the surrogate model method to approximate the functional relationship between the geometric dimensions, ultimate flexural capacity, and initial rotational stiffness of semi-rigid joints, a prediction model with high accuracy is established. Furthermore, the moment-rotation curves of semi-rigid joints in transmission towers are fitted using the Kish-Chen power function model. The results show that the proposed surrogate model-based prediction method for moment-rotation curves of semi-rigid joints can reduce the cost of experiments and numerical simulations, while accruately approximating the actual force-deformation relationship of semi-rigid joints in transmission towers. This method also provides valuable insights for the engineering design and theoretical research of semi-rigid joints in transmission towers.