The invention discloses a slowing down device provided with double planetary gear trains and used for a high-power scraper conveyer, and belongs to the field of mechanical transmission. The slowing down device comprises an input shaft, a bevel gear set, a cylindrical gear set, the first planetary gear train, the second planetary gear train and an output shaft. The bevel gear set is composed of a small bevel gear, a large bevel gear and a bevel gear set output shaft. The cylindrical gear set is composed of a small cylindrical gear, a large cylindrical gear and a cylindrical gear set output shaft. The first planetary gear train is composed of a high-speed level sun gear, a high-speed level planet gear, a high-speed level gear ring, a high-speed level planet carrier and a high-speed level output shaft. The second planetary gear train is composed of a low-speed level sun gear, a low-speed level planet gear, a low-speed level gear ring and a low-speed level planet carrier. According to the slowing down device, a four-level double-planetary-gear-train slowing down scheme is adopted, the transmission ratio is increased by five to ten times compared with a two-level bevel-planet gear transmission form of an existing high-power scraper conveyer, and the slowing down device can meet the requirement for power transfer of the high-power scraper conveyer.