A connecting tube having a dust sensing function is provided. The connecting tube includes a tube element having a first air flowing passage; a body having a second air flowing passage to communicate with the first air flowing passage; a detecting sensor disposed on the second air flowing passage to detect whether the dust or dirt passes through the second air flowing passage; a lamp part to operate according to a signal outputted from the detecting sensor; a rotating part rotatably disposed on the body; a rotation driving-passage part disposed on the body to draw in an external air into the second air flowing passage and thus to rotate the rotating part; an electric generator connected to the rotating part to generate an electric power; and a muffler part to reduce noises from the rotating part and the flowing air.