A threshing cylinder coaxial speed regulation fan belongs to agricultural machinery. The outer part of a threshing cylinder shaft is sleeved with a shaft sleeve through a bearing; a fan impeller is fixedly arranged on the outer part of the shaft sleeve, a first driving wheel is fixedly arranged on the end part of one side of the threshing cylinder shaft, a fan driving wheel is fixedly arranged on the end part of one side of the shaft sleeve, a second bearing seat assembly is fixedly arranged at the side part of the first bearing seat assembly, a transmission shaft is arranged on the second bearing seat assembly, a second driving wheel and a third driving wheel are fixedly arranged on the transmission shaft, a first transmission chain or belt is sleeved with the first driving wheel and the second driving wheel, a second transmission chain or belt is sleeved with the third driving wheel and the fan driving wheel. The structure of the threshing cylinder coaxial speed regulation fan is novel, reasonable, simple and compact, small in appearance size and convenient to configure and install, large in wind speed adjusting range, simple and convenient to adjust, high in adaptability, good in operation quality and high in efficiency.