In real-world scenarios, objects and their parts inherently possess both coarse-grained differences and intricate fine-grained structural relationships. These characteristics can be formalized as knowledge, leveraged for fine-grained part comprehension. However, existing part segmentation models consistently fail to capture these complex inter-part relationships, treating parts as independent entities and disregarding object-level distinctions. To address these limitations, we propose a novel Knowledge-Guided Part Segmentation (KPS) framework. Our approach automatically extracts structural relationships between parts using a large language model (LLM) and integrates them into a knowledge graph. Subsequently, a structural knowledge guidance module employs a graph convolutional network (GCN) to model these relationships. Furthermore, a coarse-grained object guidance module captures object-specific distinctions and integrates them as visual guidance. The integrated insights from the part structure and object differentiation guide the fine-grained part segmentation. Our KPS achieves notable improvements in segmentation performance, with a 4.96\% mIoU gain on PartImageNet and a 3.73\% gain on Pascal-Part. Moreover, in the open-vocabulary setting on Pascal-Part-116, it improves hIoU by 3.25\%, highlighting the effectiveness of knowledge guidance in enhancing fine-grained part segmentation.