Abstract: By direct numerical simulation of Navier-Stokes Equations, we investigate the three-dimensional merger of two perturbed parallel vortex tubes in this paper. The pseudo-spectral method is used. It is found that the three dimensional merger takes place in the manner of twinning similar to helical pairing. It is worthy of special mention that the concentration of vorticity occurs in non-axial x and y directitions its maximum value can reach even more than 30 percent of the initial peak vorticity and it...