Real-world data often exhibit long-tailed distributions, which degrade data quality and pose challenges for deep learning. To address this issue, knowledge transfer from head classes to tail classes has been shown to effectively mitigate feature sparsity. However, existing methods often overlook class differences, leading to suboptimal knowledge transfer. While the class space exhibits a label hierarchy, similarity relationships beyond hierarchically related categories remain underexplored. Considering the human ability to process visual perception problems in a multi-granularity manner guided by semantics, this paper presents a novel semantic knowledge-driven contrastive learning method. Inspired by the implicit knowledge embedded in large language models, the proposed LLM-based label semantic generation method overcomes the limitations of the label hierarchy. Additionally, a semantic knowledge graph is constructed based on the extended label information to guide representation learning. This enables the model to dynamically identify relevant classes for learning and facilitates multi-granularity knowledge transfer between similar categories. Experiments on long-tail benchmark datasets, including CIFAR-10-LT, CIFAR-100-LT, and ImageNet-LT, demonstrate that the proposed method significantly improves the accuracy of tail classes and enhances overall performance without compromising the accuracy of head classes.