The recognition of microbial nucleic acids is a major mechanism by which the immune system detects pathogenic microorganisms. Cyclic guanosine phosphate adenosine synthase is a cytoplasmic DNA sensor that activates the CGAS-STING pathway after sensing pathogenic DNA. The cGAS-STING pathway not only mediates innate immune response against infections by a large variety of DNA-containing pathogens, but also senses tumor-derived DNA to generate intrinsic antitumor immunity. However, aberrant activation of the cGAS-STING pathway by autologous DNA can also lead to autoimmune and inflammatory diseases. The paper reviews the cGAS-STING signaling pathway and its regulation and functions in antiviral innate immunity, and expounds the role of the cGAS-STING signaling pathway in defensing viral infections and diseases.