A simple inclined-hole drilling jig comprises a jig body having a crossover plane at the bottom to evenly press against the wood workpiece, and a beveled end member at the front concavely disposed with a guiding shaft hole extending downwardly from the beveled end member through the crossover plane. The upper end of guiding shaft hole is configured with a guide bushing for drill bit to pass through. The rear end and side surfaces of jig body are respectively formed with a reference face and sidewalls perpendicular to the crossover plane; the sidewall is at least concavely disposed with a dust guide groove intercrossing the guiding shaft hole and slidingly disposed with a graduated extension board to allow axial displacement and positioning. The end of the extension board is bent to form a retaining end plane parallel to the reference face to extendingly adjust the axle spread of reference face.