The invention discloses a multi-beam coaxial laser damage threshold test device and a realization method. According to the multi-beam coaxial laser damage threshold test device, four high-energy pulsed lasers are adopted, reflected by corresponding prisms and then enter a coaxial optical system, four light beams use one set of system and a computer control processing system, a variable-interval positive lens and a variable-interval negative lens are utilized to constitute a beam expanding system, the optical interval of the beam expanding system is adjusted, and thus collimated beam expandingof laser beams with different wavelengths can be achieved; and a stepper motor is adopted to precisely control the position of a focusing lens, and focal lengths of the different laser wavelengths arecompensated, so that it is ensured that laser is transmitted to the test surface, and the size and defocusing amount of a light spot are constant. According to the multi-beam coaxial laser damage threshold test device, integration, automation and intellectualization of a test system are achieved, thin film damage can be judged quickly and accurately in real time online, and laser damage thresholds of the various different wavelengths can be measured through the same test device.