With the extensive application of PCR technology and DNA sequencing technology, analysis of molecular data has become increasingly important in biological research. That genomic DNA contains rich genetic information renders nuclear markers or combination of nuclear and mitochondrial markers as useful means to study insect phylogeny. For the internal transcribed spacer (ITS) possesses moderate length, fast evolutionary rate, and especially is easy to amplify, it has been widely used as a genetic marker in insect phylogenetic research. In this paper, we briefly introduce its structure and characteristics, summarize its application in rapid identification of closely related species and species status, insect phylogeny at genus or higher levels, and insect phylogeography, and discuss its research prospects.