Abstract: Defoliants are agrochemicals that promote leaf abscission by regulating crop physiological metabolism. Based on their mechanisms of action, they are categorized into two major types: hormone-based and herbicide-based defoliants. These compounds are widely applied in cotton, wheat, and oilseed rape to facilitate leaf drop and crop maturation, playing a critical role in modern mechanized harvesting systems. This article systematically reviews the classification, mechanisms of action, current registration status, application practices, and environmental safety of defoliants in China, while also discussing future prospects. Studies indicate that the impact of defoliants on crop yield and quality is influenced by factors such as product type, application dosage, timing, and frequency, necessitating scientific selection and standardized practices. However, current research on risk assessment remains insufficient. Long-term and large-scale use may pose risks of environmental residue and phytotoxicity to subsequent crops, highlighting the urgent need for further research to ensure agricultural ecological security and product quality.