Abstract： Insomnia is one of the common diseases in clinical diagnosis and treatment. Its pathogenesis is complex and diverse，which mainly consists of three main symptoms： difficulty in falling asleep，short sleep time and easiness in waking up. It will imperceptibly affect the emotion，daily work and study state of patients，greatly reducing their life happiness. By focusing on the theory that "defensive qi cannot pass from yang to yin" in Huangdi Neijing，this paper points out the correlation between insomnia and the spleen， the stomach and defensive qi， and expounds the proposition that "the spleen governs defensive qi"，and also discusses the pathogenesis of insomnia based on this proposition. It is pointed out that the theory of "the spleen governing defensive qi" can be used to guide and provide a new idea for the clinical treatment of insomnia.