The fermentation dynamics and bacterial diversity of mixed lucerne (LU) and sweet corn stalk (SS) silage ensiled at six ratios were evaluated. LU and SS, harvested at 187 and 222 g/kg dry matter, respectively, were chopped to a length of about 1 cm and mixed in the fresh weight proportions of 10:0, 8:2 (Mix 1), 6:4 (Mix 2), 4:6 (Mix 3), 2:8 (Mix 4) and 0:10. Silos of each ratio were prepared in triplicate and stored at ambient conditions for 5, 10, 15, 30 and 65 days. The fermentation profile of silage during storage was determined at each point, and the bacterial diversity of silage stored for 65 days was analysed by high‐throughput sequencing. The silages with more SS inclusion in the forage mixtures were higher in lactic acid and lower in butyric acid and ammonia N, regardless of storage time. After 65 days of storage, Lactobacillus (relative abundance, 91.36%–95.86%) dominated the bacterial community in Mix 3, Mix 4 and SS silages, whereas the community composition in LU, Mix 1 and Mix 2 silages was complex, mainly consisting of Lactobacillus (45.48%–61.01%), Enterobacter (11.09%–19.57%) and Weissella (10.44%–14.13%). Inclusion of SS significantly enhanced the fermentation characteristics, and remarkably improved the bacterial community structure, reflected by increasing the relative abundance of Lactobacillus and reducing the relative abundance of Enterobacter and Pantoea. The fermentation quality was better when LU was ensiled in a mixture with ≥ 40% SS.