  In this article, we consider the properties of hitting times for
$G$-martingale and the stopped processes. We prove that the stopped processes
for $G$-martingales are still $G$-martingales and that the hitting times for a
class of $G$-martingales including $G$-Brownian motion are quasi-continuous. As
an application, we improve the $G$-martingale representation theorems in
[Song10].
