Abstract: To study the flavor changes of potato thick juice beverages before and after fermentation with compound probiotics, this experiment used SPME-GC-MS detection technology to identify the volatile compounds in unfermented (WF), fermented (FJ), and post-fermented (HS) potato thick juice samples. The results showed that a total of 57 volatile substances were detected in the three groups of samples, including 22 alcohols, 6 aldehydes, 4 acids, 8 esters, 9 ketones, and 8 others. Through PCA score plots, loading plots, and cluster heat maps of the volatile compound contents and types, it was found that the main volatile substances in HS samples were alcohols, ketones were the main volatile substances in FJ samples, and aldehydes and esters had relatively high contents in WF samples, which also contained rich acid substances. By comparing and analyzing the key flavor substances before and after the fermentation of thick juice through ROAV, it was found that the key flavor substances in HS and FJ samples were roughly the same, both being 2-nonanone and 2-undecanone, while 1-octen-3-ol and benzaldehyde were the main substances in WF samples. The results of this study provide a scientific basis for the development and flavor improvement of fermented potato thick juice.