Insects compose more than half of all living organisms on earth, playing essential roles in global ecosystems and forming complex relationships with humans. Insect research has significant biological and practical importance. However, the application of genetic manipulation technology has long been restricted to several model insects only, such as gene knockout in Drosophila, which has severely restrained the development of insect biology research. Recently, with the increase in the release of insect genome data and the introduction of the CRISPR/Cas9 system for efficient genetic modification, it has been possible to conduct meaningful functional studies in a broad array of insect species. Here, we summarize the advances in CRISPR/Cas9 in different insect species, discuss methods for its promotion, and consider its application in future insect studies. This review provides detailed information about the application of the CRISPR/Cas9 system in insect research and presents possible ways to improve its use in functional studies and insect pest control.