  The mechanism of recombination of intersecting D-branes is investigated
within the framework of effective tachyon field theory. We regard the branes as
the kink-type tachyon condensed states and use the effective two-tachyon
Lagrangian to study the off-diagonal fluctuations therein. It is seen that
there is a tachyonic mode in the off-diagonal fluctuations, which signs the
instability of the intersecting D-branes. We diagonalize the two-by-two
tachyonic matrix field and see that the corresponding eigenfunctions could be
used to describe the new recombined branes. Our prescription can be extended to
discuss the general behavior of the recombination of intersection D-branes with
arbitrary shapes. We present in detail the physical reasons behind the
mathematical process of diagonalizing the tachyonic matrix field.
