The engineering structural components have been widely used, while the defects emerged from manufacturing, processing and service are inevitable, therefore the employing of intelligent self- healing materials has become an essential way to improve the service life and reliability of the components. This study introduced the current state- of- the- art of the application of microcapsules in various composite materials, and the research progress of the mechanical properties and healing efficiency evaluation indexes of microcapsule- based intelligent self- healing composites were briefly described. Then, the triggering mechanism of microcapsules in composite was classified, and the self- healing mechanism of microcapsules was reviewed based on theoretical analysis, numerical simulation and experimental research respectively. Finally, the problems of the current research on microcapsules were analyzed and the future development trend was foreseen to provide reference for the promotion and application of self-healing composites.