Methods： The Lactobacillus plantarum X19-2D with strong protein decomposition ability were inoculated into mutton fermented sausages， and natural fermentation and inoculation of commercial starters were used as controls. Study changes on amino nitrogen， free amino acids， protein content and volatile salt-based nitrogen（TVB-N） in fermented sausages. Objective： Study the effects of Lactobacillus plantarum on protein decomposition and free amino acids released in fermented sausages. Results： In 11 days and 90 days of storage， the contents of amino nitrogen in the X19-2D group was significantly higher than natural fermented group （P<0.05）. During the storage period， the contents of total free amino acids and flavor amino acids in the X19-2D group were higher than those of the other two groups， and essential amino acid pattern is closer to nutritional recommendations than the other two groups. There was no significant difference on protein content between 3 groups of sausages （P>0.05）. In addition， in 11 days and 90 days of storage， the TVB-N contents of the X19-2D group was significantly lower than other two groups （P<0.05）. Conclusion： The L. plantarum X19-2D can promote mutton fermented sausage protein decomposition and non-volatile flavor production， amino acid composition is more beneficial to human absorption， and can improve product safety to some extent.