Io's plasma wake was treated as a tail of magnetic flux tubes perturbed by Io successively. The evolution of an Io-perturbed flux tube was studied numerically via magnetohydrodynamics (MHD) approach of a thin filament. Our simulations suggest that the mechanism for producing wake aurora could not be explained by either Alfvin wave or electric circuit alone, rather, the underlying physics possesses the characteristics typical for both Alfvin wave and corotational lag models. An upstream-coming flux tube must be in contact with Io for approximately 500 s, until a tilt angle of about 40 has been developed, before it is released downstream. A magnetic field depression forms downstream as a result of the continual departure of the flux tubes from Io, which in turn has significant influence on the motion of a flux tube. A perturbed flux tube would undergo a subcorotational motion in Io's plasma wake. This motion is inevitably modulated by Alfvin wave bouncing back and forth between the equatorial plane and the boundary of Io plasma torus. The scale of the subcorotation region is in the order of 1 Jovian radius (R J ). The distribution of the simulated field-aligned currents downstream is consistent with the observed wake aurora brightness profile; in particular, the periodic structure in the current distribution is in agreement with recent infrared and FUV observations showing the presence of secondary spots in the auroral emissions.