A coupling for a reflectivity-measuring device connects a first shaft of a reflectivity-measuring device with a second shaft of a motor. The first shaft inserts into a first hole of a main portion of the coupling, and the second shaft inserts into a second hole of the main portion. The-main portion further comprises a third hole communicating with the first hole, a fourth hole communicating with the second hole; a first non-skid member and a second non-skid member. The first non-skid member inserts into the third hole and abuts the first shaft located inside the first hole. The second non-skid member inserts into the fourth hole and abuts the second shaft located inside the second hole.