Objective： The preparation of Bifidobacterium lactobacillus Probio-M8 microcapsules by vacuum low temperature spray drying was studied in this paper. Methods： The optimum process conditions were determined by single factor， orthogonal experiments and Box-Behnken response surface tests. The changes in the fatty acid composition of the bacterial cell membrane before and after drying was analyzed by the gas chromatographic analysis. The impact of vacuum low temperature spray drying on the membrane integrity was investigated by the flow cytometry. The microcapsule morphological structure was observed through scanning electron microscopy. And the glass translation temperature of this microcapsule was determined by the differential scanning calorimetry. Results： It was found that the optimum spray processing parameters were inlet air temperature of 80 ℃， material flow of 9 mL/min and nozzle diameter of 1.5 mm； the best formulation of protective agent was 13% skim milk， 10% maltodextrin and 7% monosodium glutamate. Under the optimum conditions of spray drying， the survival rate of Probio-M8 was 78.34%， the microcapsule had complete structure and its state was glassy at room temperature， the integrity of cell membrane was also significantly improved. After drying， the UFA/SFA ratio of fatty acids in cell membrane increased by 0.44， maintaining the fluidity of the cell membrane. Conclusion： By optimizing the process conditions， this experiment significantly maintained the biological activity of the bacteria， and provided a technical scheme for the Probio-M8 microcapsules with low energy consumption and high activity.