  The phase transition of the Gauss-Bonnet AdS black hole has the similar
property with the van der Waals thermodynamic system. However, it is determined
by the Gauss-Bonnet coefficient {\alpha}, not only the horizon radius.
Furthermore, the phase transition is not the pure one between a big black hole
and a small black hole. With this issue, we introduce a new order parameter to
investigate the critical phenomenonand to give the microstructure explanation
of the Gauss-Bonnet AdS black hole phase transition. And the critical exponents
are also obtained. At the critical pointof the Gauss-Bonnet AdS black hole, we
reveal the microstructure of the black hole by investigating the thermodynamic
geometry. These results perhaps provide some certain help to deeply explore the
black hole microscopic structure and to build the quantum gravity.
