  In this paper, we prove that any $\kappa$-noncollapsed gradient steady Ricci
soliton with nonnegative curvature operator and horizontally $\epsilon$-pinched
Ricci curvature must be rotationally symmetric. As an application, we show that
any $\kappa$-noncollapsed gradient steady Ricci soliton $(M^n, g,f)$ with
nonnegative curvature operator must be rotationally symmetric if it admits a
unique equilibrium point and its scalar curvature $R(x)$ satisfies
$\lim_{r(x)\rightarrow\infty}R(x)f(x)=C_0\sup_{x\in M}R(x)$ with
$C_0>\frac{n-2}{2}$.
