Lepidopteran insects, as major agricultural pests, engage in a complex molecular dialogue with their host plants. Their oral secretions (OS), a mixture of saliva from salivary glands and digestive fluids from the gut, are introduced into plant tissue during larval feeding, thereby influencing plant defense responses. Through long-term co-evolution with host plants, lepidopteran insects have been able to produce OS containing a sophisticated array of components, including both elicitors that activate plant defenses and effectors that suppress them. This review systematically summarizes recent research advances in the interaction systems between lepidopteran insects and plants, with a focus on the composition, functions, and mechanisms of action of salivary proteins. Additionally, it highlights current limitations in research methodologies, such as techniques for identifying salivary proteins, understanding transmembrane transport mechanisms, and assessing functional conservation. Future studies should integrate multi-omics technologies, cross-species comparisons, and multi-host plant systems to further elucidate the evolutionary and functional diversity of lepidopteran salivary proteins, providing a theoretical foundation for developing novel pest control strategies.