The application of antigen testing is widely used in the diagnosis of COVID-19 and antigen tests have also been simplified for everyday use due to their convenience and operational capabilities. Colloidal gold nanoparticles are an important component in most antigen tests. This paper summarizes the principles and characteristics of colloidal gold nanoparticles mainly by reviewing a large amount of literature and also performs antigen testing and observes the development process, thus validating the theoretical aspects. In this paper, it was found that colloidal gold nanoparticles can react with viruses and produce visible results on immunochromatographic test paper. However, when the concentration of the virus is insufficient, visualization effect may not be discernible to the naked eye. This is the reason why antigen testing is not as accurate as nucleic acid testing. Therefore, antigen testing is more suitable for home-based daily testing. This article has helped to understand the role of colloidal gold nanoparticles in immunochromatographic test strips, which in turn aids in improving the accuracy of these test strips.