The grasp generation of dexterous hand often requires a large number of grasping annotations. Especially for functional grasp-requiring the grasp pose to be convenient for the subsequent use of the object. However, annotating high DoF dexterous hand pose is rather challenging. This prompt us to explore how people achieve manipulations on new objects based on past grasp experiences. We find that people are adept at discovering and leveraging various similarities between objects when grasping new items, including shape, layout, and grasp type. In light of this, we analyze and collect grasp-related similarity relationships among 51 common tool-like object categories and annotate semantic grasp representation for 1768 objects. These data are organized into the form of a knowledge graph, which helps infer our proposed cross-category functional grasp synthesis. Through extensive experiments, we demonstrate that the grasp-related knowledge indeed contributed to achieving functional grasp transfer across unknown or entirely new categories of objects. We will publicly release the dataset and code to facilitate future research.