The invention discloses an on-line monitoring device for inclination of a disconnecting switch supporting frame, and solves the difficulty in on-line real-time monitoring of the inclination of the disconnecting switch supporting frame. A gap (3) which is shaped like half a Chinese character KOU is formed in the center of the inner side of a semicircular supporting base plate (2); monomer hydraulic supporting columns (4) and a horizontal tray (5) are fixedly arranged on the top surface of the semicircular supporting base plate (2); a semicylindrical barrel body (6) is fixedly arranged on the horizontal tray; a liquid capacitor is arranged in the semicylindrical barrel body (6); a pressure measurement device is arranged on the vertical surface of a triangular-prism-shaped slot (7); a disconnecting switch supporting frame vertical column (1) is arranged in the gap (3) formed in the center of the inner side of the semicircular supporting base plate (2); the inner side surface of a contact pin swing rod (15) presses against the side surface of the disconnecting switch supporting frame vertical column (1). The on-line monitoring device is simple in structure and convenient for on-site combination, so that the aim of measuring the inclination of the disconnecting switch supporting frame immediately and accurately is achieved.