At present, there are many decision-making methods for expressway soft-foundation treatment, which are widely used in engineering. By comprehensively evaluating technical, economic, environmental, and construction aspects, these methods select the optimal solution from the point of preferred selection. However, the evaluation indexes of these methods are fuzzy, the result of decision-making is single, and the adaptability is weak. Taking the engineering cases with significant effect as standard and the objective 6 parameter as evaluation indexes, a decision model for expressway soft foundation treatment based on the similarity of cobweb structure is established. The proposed method is improved from the traditional case-based reasoning method as follows: 1) Considering the non-linear relationship between the change of the parameter value and the influence of the target effect, a non-linear standardized processing method of the index parameter is proposed; 2) Utilizing the area and shape difference of cobweb structure, a new similarity calculation method is used to evaluate the closeness between source case M and target case O. Finally, taking a domestic expressway soft foundation treatment project as an example, the comparison between the proposed method and the traditional method is carried out. The results show that the proposed method has a high matching degree, which verifies the reliability of the model. The model is convenient in computation and the result is objective, which provides an new method in soft foundation decision-treatment.