A strong edge-coloring of a graph G is a proper edge-coloring such that every path of length 3 uses three different colors. The strong chromatic index of G, denoted by chi(s)'(G), is the least possible number of colors in a strong edge-coloring of G. Let G be a graph, mad(G) be the maximum average degree and delta be the maximum degree of G. In this paper, we prove that if delta >= 6 and mad(G) < 23/8 , then chi is(G) = 7 and mad(G) < 26/9 , then chi is(G) 7 and mad(G) < 3, then chi is(G)
