For the purpose of producing high quality silage, water hyacinth silage and water hyacinth & corn straw mixed silage were studied. Water hyacinth & corn straw were mixed into 5 silages with their weight ratio of 80:20, 70:30, 60:40, 50:50 and 40:60, besides water hyacinth silage. Water hyacinth silage and mixed silage with CON，corn straw fermented green juice (FGJC)，water hyacinth fermented green juice (FGJW)，formic acid (FA)，foraform (FOR) were ensiled to study the effect of the additives. Each treatment was two repeats. Silages were fermented for 60 days under normal temperature. Then the pH value, dry matter rate（DMR）, gas loss rate（GLR）, ammonia nitrogen（NH3-N）, and other items were measured. The result showed that the four additives significantly affected the fermentation quality of silages. The effect of FGJC and FGJW to the mixed silages with 80:20 mixed ratio was the best. The fermentation quality of mixed silages with additives was better than water hyacinth silages. Preparing of water hyacinth & corn straw mixed silages is a good way to utilize water hyacinth.