In order to provide reference for probiotics application in aquaculture, Bacillus subtilis （A）, Streptococcus faecalis （B） and photosynthetic bacteria （C） were prepared according to the ratios of 9：1, 4：1, 1：1, 1：4 and 1：9 with 10^5 cfu/ml as the unit of concentration into 15 mixed microecological preparations, and their effects on COD, ammonia nitrogen, nitrite nitrogen and sulfide in pond water were investigated. The results showed that the mixed preparation of B. subtilis and photosynthetic bacteria at a ratio of 1：4 had the best effect in treating COD （P〈0.05）, the mixed preparation of B. subtilis and S. faecalis at a ratio of 4：1 showed the best effect in treating ammonia nitrogen （P〈0.05）, the mixed preparation of S. faecalis and photosynthetic bacteria at a ratio of 4：1 showed the best effect in treating nitrite nitrogen （P〈0.05）, and the mixed preparation of Streptococcus faecalis and photosynthetic bacteria at a ratio of 9：1 had the best effect of reducing sulfide （P〈0.05）.
