Abstract: The principle and techniques of positron annihilation including positron annihilation lifetime spectroscopy and coincidence Doppler broadening are introduced in this article.Based on the experience of recent research the application of positron annihilation techniques in the study of age hardening aluminium alloy is reviewed.The methods to detect the change of micro structure of aluminium alloy in age-hardening and to describe the solute aggregation kinetics and give information on vacancy-solute interaction by means of positron annihilation techniques are described.