A GU24 3-way dimmer knob-type switch lamp holder is disclosed, where the body of the lamp holder is provided with three contact plates at the two sides of its interior and on its bottom. And an insulating rotor and a rotor conducting plate therein is driven by a knob. The rotor conducting plate is shaped into four portions along its rim, where three of them come with a shaped contact plate, while the fourth is void. The insulating rotor and the rotor conducting plate are driven to rotate by turning the knob, which enables three contact plates in the body and three contact plates of the rotor conducting plate to form no conduction or different conduction modes that enable various levels of illumination: dim, moderate and high brightness after power ON and feature power OFF as well.