Since the elucidation of the photoperiodic regulation of diapause in the eggs of the silkworm, Bombyx mori, and in the locust, Acrydium arenosum, in 1933, there have been over 90 years of research on insect diapause. This review summarizes the core scientific advancements in research on the regulation of insect diapause in China since the beginning of the 21st century, including: (1) Physiological and ecological mechanisms involved in environmental factors of photoperiod- temperature synergy; (2) Physiological metabolic regulation during diapause induction, maintenance, and termination; (3) Molecular switch mechanisms across different developmental stages (egg/embryonic, larval, pupal, and adult diapause). Prospects for future research are also presented. Deepening mechanistic understanding of diapause regulation will facilitate: (a) The discovery of novel molecular targets for diapause-based pest management; (b) The development of population monitoring models based on diapause characteristics; (c) The optimization of ecological management strategies for major pests, while at the same time, providing a theoretical foundation for the conservation and utilization of beneficial pollinators, predatory and parasitic insects, and other insect resources. This review aims to offer comprehensive references for both theoretical and applied research on insect diapause.