The complex pore structure of unconventional reservoirs is an important factor affecting reservoir properties and hydrocarbon storage. At present，there are many methods for characterizing the pore structure of unconventional reservoirs，but the principles and application scopes for these techniques are quite different. The main characterization techniques of unconventional reservoir pore structure are reviewed from qualitative and quantitative aspects. The progress and application of current techniques are summarized，including two-dimensional scanning electron microscope（SEM）image characterization technique，three-dimensional micro-nano CT reconstruction technique，indirect quantitative characterization technique such as nitrogen adsorption experiment，and full-aperture joint characterization technique which is widely studied at present. The applicability of different characterization methods is clarified in terms of characterization principle，object and precision，and the characterization system for reservoirs with different pore scale is formed，which basically meets the requirements of unconventional reservoir evaluation. However，the current unconventional reservoir pore structure characterization techniques still need further exploration in terms of accuracy and scale，as well as joint characterization algorithm interpretation.