A clamping mechanism includes an adjusting assembly, a driving assembly and a plurality of clamping assemblies. Each clamping assembly includes a base body slidably sleeved on the driving assembly. The adjusting assembly includes a first adjusting member, and a second adjusting member parallel to the first adjusting member. The first adjusting member is fixed to a base body located on a first end of the plurality of clamping assemblies. Opposite ends of the second adjusting member are fixed to the driving assembly and a base body located on a second end of the plurality of clamping assemblies. Each of the first and second adjusting members respectively define a plurality of first and second steps. The first steps and the second steps slidable resist sidewalls of the base body. An upward direction of the plurality of first steps is reverse to that of the plurality of the second steps.