▎ 摘　　要

The integer quantum Hall effect is studied for a non-interacting electron in a monolayer graphene. We numerically calculate the Hall conductivity in a single Landau level with disorder, and estimate the critical energies for the extended states in thermodynamic limit. We show that a valley-degenerated (K and K') Landau band has extended levels at two different energies, indicating that an extra Hall plateau appears inside.