A strong edge-coloring of a graph $G$ is an edge-coloring in which every color class is an induced matching, and the strong chromatic index $χ_s'(G)$ is the minimum number of colors needed in strong edge-colorings of $G$. A graph is $2$-degenerate if every subgraph has minimum degree at most $2$. Choi, Kim, Kostochka, and Raspaud (2016) showed $χ_s'(G) \leq 5Δ+1$ if $G$ is a $2$-degenerate graph with maximum degree $Δ$. In this article, we improve it to $χ_s'(G)\le 5Δ-Δ^{1/2-ε}+2$ when $Δ>4^{1/(2ε)}$ for any $0<ε<1/2$.