The invention discloses a ball valve opening and closing state indicating device which comprises a mounting ring (1), an angle-square-shaped flag pole (2) and a flag (3). The vertical segment of the flag pole (2) is connected to the mounting ring (1) in an inserted manner. The horizontal segment of the flag pole (2) is connected to one side of the flag (3). The flag (3) is composed of a fold (4) and two sector faces (5). Three rubber rings (6) are arranged on the other side of the flag (3). A label (7) with a closing indicating meaning is arranged on the outer side of each sector face (5) of the flag (3), and a label (8) with an opening indicating meaning is arranged on the inner side of each sector face (5) of the flag (3). By means of the posture of the flag (3) and the seen labels (8) with the opening indicating meaning or the seen labels (7) with the closing indicating meaning, the opening and closing state of a ball valve is visually known.