The invention discloses a speed 
reducer provided with an 
air cooling, oil collecting, lubricating and clearance eliminating structure. The speed 
reducer comprises a speed 
reducer shell, a 
gear transmission mechanism, an 
air cooling device and an oil collecting device. The 
air cooling device comprises a draught fan, an 
air filter and an oil-gas separator. The speed reducer further comprises a first belleville spring used for applying 
axial thrust to a first 
bevel gear and a second belleville spring used for applying 
axial thrust to a fourth 
bevel gear. The oil collecting device comprises a circular 
pipe body, a partition board, an 
oil storage cavity, an oil inlet and an oil outlet. According to the speed reducer, the gears and lubricating oil in the speed reducer shell are cooled through the air cooling device, and thus the problems that due to long-term working of the speed reducer, the temperature of the lubricating oil is increased, and the performance is reduced can be solved; in addition, when the gears are abraded, the belleville springs can automatically push the first 
bevel gear and the fourth bevel gear to move in the axial direction, and thus a gear fit clearance caused by frictional abrasion is eliminated; furthermore, the lubricating oil is carried into a gear engagement area through the oil collecting device to lubricate the gears, and thus the lubricating and cooling effects on the gears can be improved.