As conventional transmission mechanism is difficult to realize coaxial rotation transmission in a narrow radial space,a coaxial transmission mechanism based on cylindrical cams is proposed.On the basis of the structure of a lens, the transmission mechanism is combined by two cylindrical cams,and one is initiative cam and the other is passive cam. Spiral slots are opened on the surface of both cams. When the spiral lead of the passive cam is n times that of initiative cam, the transmission mechanism can offer a transmission ratio of n. Transmission efficiency and transmission accuracy are analyzed and the relation between the angle of initiative cam’s spiral slot and the transmission efficiency and transmission accuracy is discussed. An experiment is performed to test transmission accuracy, which shows the transmission ratio accuracy is less than 1.6%. Obtained mechanism has compact structure,high accuracy and can be locked automatically.