The invention relates to a shifting clamping mechanism of safety valves. The mechanism comprises a base frame, wherein a base disc is arranged at the upper end of the base frame; an air inlet disc is arranged at the middle part of the base disc; an air inlet hole is arranged on the air inlet disc; the air inlet hole is connected with the air inlet pipe; the shifting clamping mechanism is characterized in that a portal frame is arranged at each of two sides of the base disc; a cylinder guide track is erected at the upper end of the portal frame; two hydraulic cylinders or air cylinders which can move left and right are arranged on the cylinder guide track; a clamping disc for holding the safety valve is arranged at the end part of a piston rod of each of the hydraulic cylinders or air cylinders; and a plurality of sealing rings are wound on the base disc. The shifting clamping mechanism is used on a safety valve testing table in match; therefore, the problem of clamping sealing (air inlet sealing) of safety valves of different specifications and models during testing can be solved efficiently, and the operation personnel are replaced for transport of the safety valves, and the working condition of the safety valve test is improved.