The utility model discloses a coal mine belt conveyor mechanical automatic spraying device and a conveyor thereof. The spraying device comprises a carrier roller (1) in contact with the surface of a bottom belt of the belt conveyor, wherein the first roller mechanical air valve switch (3), the first air pipe (7), the second roller mechanical air valve switch (5), the second air pipe (8), the pneumatic ball valve (6), the water inlet pipe (9), the water outlet pipe (10), the cam rotating mechanism (4), the transmission shaft (11) and the transmission shaft fixing frame (2) are connected with the cam rotating mechanism (4) and the carrier roller (1). A belt of the belt conveyor drives the carrier roller (1) and a roller of the cam rotating mechanism (4) to rotate synchronously; protruding points on the idler wheel alternately touch and open the first idler wheel mechanical air valve switch (3) and the second idler wheel mechanical air valve switch (5) in the rotating process to be communicated with an underground air pressure main pipe, a first air pipe (7) and a second air pipe (8), and the pneumatic ball valve (6) is opened to be communicated with a water inlet pipe (9) and a wateroutlet pipe (10) to spray water mist. Electric energy is not needed, and synchronous control over spraying and belt operation is achieved.