Immunological synapse (IS) is a specialized and sophisticated supramolecular activation cluster structure that is formed at the interface between T cell and antigen presenting cells. It is a dynamic multistage progress, involving adhesion molecules, cytokines, signaling molecules, cell cytoskeletal proteins and other molecules. IS is not only contribute to the stability of the contact between T cells and APC, but also promotes T-cell activation and proliferation through T cells signaling pathway. Studying of the immunological synapse could explain molecular mechanisms of immune activation, immune tolerance, and the mechanism of interaction between pathogenic microbes and immune cells, which will provide new ideas for further revealing the pathogenic mechanism of disease, and seeking new target molecules for disease control and prevention. Recently, optical imaging provides a powerful help for visualization on the relationship between IS formation and T-cell activation. It provides a powerful tool for studying the immune response under physiological and pathological conditions.