By inoculating Lactobacillus sake and Staphylococcus xylose, the experiment was divided into compound fermentation group, a single Lactobacillus sake group, and control by natural fermentation, the effect of different starter cultures on lipolysis, proteolysis and flavor formation in the fermented mutton sausages was explored. The results showed that the addition of compound starters promoted the rapid acidification of sausage, and the pH value of mixed group was reduced to 4.6, which was significantly lower than the safe acidity of the fermented meat products of 5.3 and other groups （P<0.05). The pH drop caused the water activity (aw) and nitrite residue in the mixed group to be significantly lower than those in the single, control and raw meat groups （P<0.05), and the redness color (a*) of the mixed group was the best. The content of free fatty acids in sausages was increased gradually. The content of monounsaturated fatty acids in sausages at the end of maturity was significantly higher than that in the single and control groups （P<0.05), and the contents of saturated and polyunsaturated fatty acids in the control group were the highest, all which indicated that the mixed starters contributed to the release of monounsaturated fatty acids, while endogenous lipase played a key role in the release of saturated and polyunsaturated fatty acids. The proteolysis showed that the proteolytic index (PI) and free amino acids content of the starter group were higher than those of the control group, but the difference was not significant （P>0.05). Totally 45 kinds of flavor substances were detected in the inoculated, which were higher than 44 kinds in the control group and 27 kinds of raw meat （P<0.05). The mixed starters improved the characteristic flavor content of the sausage, such as 3methylbutanal, aldehyde, heptaldehyde, nnonanal and other aldehydes. In summary, the addition of compound starters helped to shorten the fermentation period, increase the content of monounsaturated fatty acid, and improve the color and flavor sensory quality of sausages.