  Understanding black hole microstructure via the thermodynamic geometry can
provide us with more deeper insight into black hole thermodynamics in modified
gravities. In this paper, we study the black hole phase transition and
Ruppeiner geometry for the $d$-dimensional charged Gauss-Bonnet anti-de Sitter
black holes. The results show that the small-large black hole phase transition
is universal in this gravity. By reducing the thermodynamic quantities with the
black hole charge, we clearly exhibit the phase diagrams in different parameter
spaces. Of particular interest is that the radius of the black hole horizon can
act as the order parameter to characterize the black hole phase transition. We
also disclose that different from the five-dimensional neutral black holes, the
charged ones allow the repulsive interaction among its microstructure for small
black hole of higher temperature. Another significant difference between them
is that the microscopic interaction changes during the small-large black hole
phase transition for the charged case, where the black hole microstructure
undergoes a sudden change. These results are helpful for peeking into the
microstructure of charged black holes in the Gauss-Bonnet gravity.
