Postbiotics can be defined as soluble metabolites released by food microorganisms during the growth and fermentation in culture medium， food， or gastrointestinal tract. It is rich in bioactive substances with different molecular weights. At present， the preparation and application of postbiotics have attracted much attention. Postbiotics of lactic acid bacteria is probably obtained using MRS medium and some byproducts of animals and plants (e.g. whey culture medium) are also used as culture medium to prepare postbiotics. The cell-free supernatant with large amounts of active substances can be obtained by post-treatments， such as centrifugation， filtration， cell disruption， and so on. Therefore， the biological activity of postbiotics can be influenced by the types of bacteria， culture conditions， preparation technology and analysis methods. Adding specific functional postbiotics to food can effectively improve food quality， which is the foundation and critical point to exert their active functions. The use of analytical procedures to detect the quantity and quality of postbiotics and the antagonistic molecules can help to study postbiotic metabolites derived from lactic acid bacteria. It also can clarify the beneficial effects of postbiotic substances on food. This article summarizes the preparation methods， chemical analysis techniques and factors affecting postbiotic activity of lactic acid bacteria. It can provide the theoretical references for the further research and development of postbiotic products， and also can maximize the effect of postbiotic activity.