  An unstable torsion free sheaf on a smooth projective variety gives a GIT
unstable point in certain Quot scheme. To a GIT unstable point, Kempf
associates a "maximally destabilizing" 1-parameter subgroup, and this induces a
filtration of the torsion free sheaf. We show that this filtration coincides
with the Harder-Narasimhan filtration.
