  We study the Misner-Sharp mass for the $f(R)$ gravity in an $n$-dimensional
(n$\geq$3) spacetime which permits three-type $(n-2)$-dimensional maximally
symmetric subspace. We obtain the Misner-Sharp mass via two approaches. One is
the inverse unified first law method, and the other is the conserved charge
method by using a generalized Kodama vector. In the first approach, we assume
the unified first still holds in the $n$-dimensional $f(R)$ gravity, which
requires a quasi-local mass form (We define it as the generalized Misner-Sharp
mass). In the second approach, the conserved charge corresponding to the
generalized local Kodama vector is the generalized Misner-Sharp mass. The two
approaches are equivalent, which are bridged by a constraint. This constraint
determines the existence of a well-defined Misner-Sharp mass. As an important
special case, we present the explicit form for the static space, and we
calculate the Misner-Sharp mass for Clifton-Barrow solution as an example.
