The invention discloses a knowledge reasoning-based big data service label extension method and system, and the method comprises the steps: S1, selecting a to-be-extended label and a label subordinatekeyword set K from a preset service label tree, searching each keyword, and obtaining a result-related URL set C; S2, for each keyword, traversing a corresponding URL in the set C, obtaining text content from each webpage, performing semantic analysis on the text, extracting a semantic object and a semantic relationship associated with the keyword, and constructing a semantic relationship knowledge graph; S3, checking and screening entities in the knowledge graph by utilizing the knowledge graph and combining the ontology rule model and taking the to-be-expanded label as a basis, and adding entity attribute contents passing the check into a result set in a keyword form; S4, judging whether the scale of the result set reaches a preset extension scale or not: if so, ending, otherwise, taking the keywords in the result set as a set K, and returning to the step S1.