A kind of Bi-direction Thrust Torsion Coupling, which can convert straight movement into rotary and amplify the output torque at the same time, is designed.Combined with the Pressure Gain Mechanism of Two Dimensional (2D) Valve, 2D valve with displacement enlarging could be gotten.By using numerical calculation and experimental method, its noload input and output characteristic was studied, and the nonlinear effect caused by the backlash in the thrust torsion coupling was eliminated by dither compensation technology. Experimental result on prototyping coupling carried out shows its good stability in meshing, and its hysteresis is best down to about 1.5%, when proper dither signal of amplitude and frequency were chosen, and its input and output characteristic is basically linear. Simulation and experiment results are basically same, which show that prototyping coupling has precise position stiffness, which lay foundation for realizing displacement magnification.