  It has been proved in \cite{ge} for every $p$-group of order $p^n$,
$|\mathcal{M}(G)|=p^{\f{1}{2}n(n-1)-t(G)}$, where $t(G)\geq 0$. In \cite{be,
el, zh}, the structure of $G$ has been characterized for $t(G)=0,1,2,3$ by
several authors. Also in \cite{sa}, the structure of $G$ characterized when
$t(G)=4$ and $Z(G)$ is elementary abelian. This paper is devoted to classify
the structure of $G$ when $t(G)=4$ without any condition.
