Abstract: 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. Each treatment was two repeats. Silage 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 pH values of all the 5 mixed silages were lower than water hyacinth silage. (P<0.01), the pH value of the mixed silage 70:30, 60:40, 50:50 and 40:60 was lower than 4.2, and their NH3-N value was significantly lower than water hyacinth silage（P<0.01）. That means that the treatment of adding corn straw to water hyacinth could help to make high quality silage.