Abstract: As a micro-linear deformation measurement system, extensometers are widely used in different fields of scientific research and industrial testing. The types, working principle and precision of the existing extensometers are not the same, so it is difficult to select the appropriate extensometer accurately and effectively. The working principle, application status and trend of mechanical extensometer, electronic extensometer, video extensometer, laser extensometer and bar code extensometer were analyzed to provide reference to relevant engineers and technicians.