Objective: In order to study the effect of biotransformation of aroma producing bacteria on volatile components of Siraitia grosvenorii extract. Methods: Raoultella planticola VP4-4 was used to biotransform the extract of Siraitia grosvenorii, and the volatile component of Siraitia grosvenorii before and after fermentation were analyzed by simultaneous distillation extraction and gas chromatography-mass spectrometry（GC-MS）. Results: The main aroma components or aroma precursors in the fermentation products of Siraitia grosvenorii were hexadecanoic acid, （z）-6-octad ecenoic acid, （z,z）-9,12-octadecadienoic acid，methyl-Butanoic acid, hexanoic acid, （Z）-9-Octadecenoic acid ethyl ester, hexadecanoic acid ethyl ester, benzeneacetaldehyde, 5-methyl-2-furancarboxaldehyde, benzaldehyde, nonanal, 2-furanmethanol, Ethenyl-2-methoxy-phenol, etc. In addition, vanillin with strong milk flavor was produced by biotransformation. The number of acids increased from 6 to 11, and the relative content increased to 60.07%. The relative contents of esters, carbonyls, alkanes, alcohols and phenols were reduced to 30.72%, 4.07%, 0.81%, 0.34% and 0.29%, respectively. And the compounds increased from 50 to 64 after fermentation. Conclusion: Biotransformation endows Siraitia grosvenorii fermented products with rich natural aroma such as flower aroma, fruit sweet aroma and milk aroma, reduces the types and relative content of macromolecular irritant components, and plays a role in increasing aroma and reducing impurities.