Super-low frequency flexibility during motion is an important issue for a large space manipulator,which involves not only the bending vibration of arm exists, but also the joint torsional vibration. In joint control, what is important is to stabilize and suppress low flexible vibration of joint and arm while joint position is being controlled. How gear ratio parameters for joint structure affect vibration suppression is also a required problem to analyze in joint design of space manipulator, on which gear ratio parameters depend. Combined dynamics of flexible joint and arm for space manipulator was modeled with concentrated parameter method, one strategy of suppressing joint vibration and arm vibration simultaneously was put forward, the effect of gear ratio on vibration suppression was analyzed by numerical simulation and theoretical analysis. This will be useful in design and research of large space flexible manipulator.