The invention provides a fracture extension judging method of a hydraulic fracturing crack on a sand shale thin interbed geological interface. An existing hydraulic crack extension model is revised and improved, and a deviation angle of the hydraulic crack on the geological interface can be accurately determined according to the extension form judgment standard of the hydraulic crack on the thin interbed geological interface. The defects of the existing crack extension model in predicting extension of the hydraulic crack in a thin interbed are overcome.