With food packaging playing an increasingly important role in food quality and safety， freshness indicator materials have become a research hotspot. On the one hand， it can block the entry of microorganisms， effectively inhibit the breeding and reproduction of microorganisms， ensure the stability of the internal environment of food packaging， and then change the quality of food； On the other hand， it can monitor and indicate environmental changes inside the packaging to feed back food quality information. In this study， food grade polymer materials high lost corn starch (HAMS) and polyvinyl alcohol (PVA) were used as the main raw materials， and the compound pH indicator MR-BB (mixture of methyl red and bromothymol blue) was loaded. At the same time， nano titanium dioxide (nano-TiO₂) with high antibacterial activity was used by ultrasonic dispersion method. At the same time， the crosslinking agent glycerol and hydrophobic agent urea were used to construct the polymer three-dimensional network structure and optimize its physicochemical properties. The pH-responsive nanometer fresh-keeping- food freshness indicator material (AFIF) was prepared by solution polymerization and casting film. Based on the basic performance， the volume of high amylost corn starch and PVA was 7∶3， the amount of glycerin was 2%， and the amount of urea was 2%. By comparing the data and optimizing the sensitivity and accuracy of pH responsiveness of AFIF film， it could be seen that the optimal volume ratio of MR-BB was 1∶2 and the optimal addition amount was 6%. In this paper， the bacteriostatic performance of AFIF film and the preservation performance of commercially available milk were analyzed. When the amount of nano-TiO₂ was 0.15 g (per 100 mL membrane liquid)， the bacteriostatic rate could reach about 80%. The practical application results showed that the liquid milk of the non-antibacterial AFIF membrane group lost its edible value after 36 h of storage at room temperature， until 72 h， the liquid milk of this group lost its edible value. At this time， the detection time of AFIF film on spoiled milk was 3 min 35 s， the film color changes from blue-green (initial) to deep yellow， the initial discolouring area was 10% (film area is 9 cm2)， the completion time of discolouring was 33 min 31 s， and the color difference value could reach 5.91. AFIF film had clear function of indicating freshness and freshness of liquid milk on the market. In this paper， its mechanism was analyzed in detail based on the structure-activity relationship.