An offset twist-roller frictional transmission mechanism was designed to satisfy the high resolution， compact space， and low-cost requirements of a beam pointing device， given its small load and low-speed application characteristics. The mechanism exhibits the characteristic of a variable transmission ratio， which is realized by changing the twist angle of the driving and driven wheels. To optimize the design interval of the twist angle， the influence of the twist angle on the output characteristics of the mechanism was studied. Based on the analysis of the kinematic characteristics， force， and deformation of the mechanism， the rigid-flexible coupling dynamic model of the transmission was established. We studied the effect of twist angle on output angular velocity stability and angular displacement resolution by conducting a physical prototype experiment and multi-body dynamics simulation. The results indicate that the larger the twist angle， the larger is the fluctuation range of output angular velocity and more unstable is the transmission. The designed mechanism can realize stable transmission when the twist angle does not exceed 80°， in addition to achieving a low-speed micro-stepping motion of 0.005° （18ʺ）. Moreover， the output resolution is far better than that of the single-stage cylindrical gear transmission. The analysis yields a novel concept of employing an offset twist-roller frictional transmission mechanism in the transmission system of a beam pointing device.