A quick internal diameter gauge is characterized by comprising a measuring tube, a slider ruler and a bottom ruler, wherein the lower end of the measuring tube is perpendicularly connected to the middle of the bottom ruler, the lower end of the slider ruler is inserted into the upper end of the transparent measuring tube in a slidable matching manner, length graduation is arranged on the wall of the measuring tube, an axial chute is arranged in the middle of the tube wall, a lock notch is arranged on one side of the chute, a spring, a lock ring and a color ring are sequentially arranged inside the measuring tube from bottom to top, and a positioning screw penetrating through the chute and capable of vertically sliding in the chute is radially arranged on the lock ring. The quick internal diameter gauge has the advantages that sum of a color mark of the color ring on the inner wall of the measuring tube and the slider ruler is the internal diameter of a measured pipeline, and the quick internal diameter gauge can realize quick internal diameter measurement of equipment and pipelines which have narrow spaces and are not available for access of a head and visual contact with a measured position.