  In most cases, to observe quantized Hall plateaux, an external magnetic field
is applied in intrinsic magnetic topological insulators $\mathrm{MnBi_2Te_4}$.
Nevertheless, whether the nonzero Chern number ($C\neq 0$) phase is a quantum
anomalous Hall (QAH) state, or a quantum Hall (QH) state, or a mixing state of
both is still a puzzle, especially for the recently observed $C=2$ phase [Deng
\textit{et al}., Science \textbf{367}, 895 (2020)]. In this Letter, we propose
a physical picture based on the Anderson localization to understand the
observed Hall plateaux in disordered $\mathrm{MnBi_2Te_4}$. Rather good
consistency between the experimental and numerical results confirms that the
bulk states are localized in the absence of a magnetic field and a QAH edge
state emerges with $C=1$. However, under a strong magnetic field, the lowest
Landau band formed with the localized bulk states, survives disorder, together
with the QAH edge state, leading to a $C=2$ phase. Eventually, we present a
phase diagram of a disordered $\mathrm{MnBi_2Te_4}$ which indicates more
coexistence states of QAH and QH to be verified by future experiments.
