  Fidelity and fidelity susceptibility are introduced to investigate the
topological superconductors with end Majorana fermions. A general formalism is
established to calculate the fidelity and fidelity susceptibility by solving
Bogoliubov-de Gennes equations. It is shown that the fidelity susceptibility
manifest itself as a peak at the topological quantum phase transition point for
homogeneous Kitaev wire, thus serves as a valid indicator for the topological
quantum phase transition which signals the appearance of Majorana fermions. The
effect of disorders is investigated within this formalism. We consider three
disordered systems and observe fidelity susceptibility peak in all of them. By
analyzing the susceptibility peak, we notice that the local potential disorders
and the hopping disorders can shift the phase transition point, while
off-diagonal disorders have no obvious influence. Our results confirm that the
existence of topological quantum phase transition is robust to these disorders,
while the behavior of the phase transition might be influenced by disorders.
