The stability of probiotic powder during storage is an important factor for its industrial application. Objective： The Bifidobacterium lactis A04 （A04） probiotic powder was obtained by freeze drying. The changes of water， bacterial morphology of A04 freeze-dried powder at different storage temperatures and its influence on the survival of A04 strain were accessed. Method： six batches of A04 freeze-dried powders with different initial viable cell counts were selected， sealed in aluminum foil bags and stored at 4， 25， 37 ℃ for 105 days， respectively. Changes in water content， water activity， water distribution， bacterial morphology and viability of A04 powders were monitored. Pearson correlation analysis was performed on the monitoring results using SPSS software. Results： No matter what the storage temperature was， the water content of freeze-dried A04 powder did not change during storage for 105 days， but the water activity of A04 powder was significantly increased during storage at 25 ℃ and 37 ℃. The results of correlation analysis showed that the loss of viable cells was positively correlated with storage temperature and water activity during storage. When the water activity was between 0.03 and 0.1， the A04 powder had well storage stability. Damage to bacterial cell envelope was observed during storage， and the degree of cell damage was increased with the increase of storage temperature and storage time， and even partial cell lysis was observed. Conclusion： The survival of probiotic bacteria during storage was negatively correlated with the storage temperature as well as water activity， and the inactivation of bacteria was correlated with the damage of bacterial cells. Therefore， it is beneficial to prolong the shelf life of probiotic powders to control the probiotic powder in low water activity and keep it relatively stable.