  We study the flow equation for the $\mathcal{N}=1$ supersymmetric $O(N)$
nonlinear sigma model in two dimensions, which cannot be given by the gradient
of the action, as evident from dimensional analysis. Imposing the condition on
the flow equation that it respects both the supersymmetry and the $O(N)$
symmetry, we show that the flow equation has a specific form, which however
contains an undetermined function of the supersymmetric derivatives $D$ and
$\bar D$. Taking the most simple choice, we propose a flow equation for this
model. As an application of the flow equation, we give the solution of the
equation at the leading order in the large $N$ expansion. The result shows that
the flow of the superfield in the model is dominated by the scalar term, since
the supersymmetry is unbroken in the original model. It is also shown that the
two point function of the superfield is finite at the leading order of the
large $N$ expansion.
