Elaborating on the definitions of coaxiality between mechanical structures, coaxiality between optical axes, and coaxiality between optical axes and mechanical axes. It introduces the principles and advantages and disadvan? tages of coaxiality measurement methods for mechanical structures, such as extensometer coaxiality measurement method, strain gauge coaxiality measurement method, dial gauge coaxiality measurement method, coordinate measuring machine coaxiality measurement method, laser alignment instrument method, etc; Analyzed the characteristics of optical axis coaxiality measurement methods such as interference comparison measurement, reflective centering measurement, and di? rect transmission measurement; This article introduces the principle and application of a coaxiality measurement method between optical and mechanical axes based on image processing and machine vision technology. It is pointed out that the measurement method for coaxiality between mechanical structures is relatively traditional, which has disadvantages such as low measurement efficiency and the need for human judgment; Coaxiality measurement technology will develop to? wards high precision, automation, and non?contact.