Based on the biology principle that microbial populations such as nitrifying bacteria and poly-P bacteria are distributed in natural waters and like to adsorb on the solid surface to form biofilm and absorb ammonia nitrogen, nitrite nitrogen, phosphorus and other nutrients to reproduce and grow, a cylindrical (R=75cm, H=100cm) in-situ purification device for aquaculture water composed of a bracket buoyancy system, a microbial attachment base, an upwelling system, a phosphorus fixing zone and a photovoltaic power generation system was developed. The results showed that upon the completion of biofilm, in the device with fresh water (22-25℃) and seawater (27-31℃) in which the ammonia nitrogen concentration was 1 mg/L, 3 mg/L and 5 mg/L, the daily reduction of ammonia nitrogen was respectively 304.587 g, 283.748 g, 314.753g and 247.274 g, 261.756 g, 282.721 g, and the daily reduction of total phosphorus was respectively 0.485 g, 0.427 g, 0.462 g and 0.566 g, 0.595 g, 0.493 g, showing strong reduction ability of ammonia nitrogen and total phosphorus. The daily reduction of ammonia nitrogen was not significantly different among the 3 fresh water groups (P>0.05) but significant among the 3 seawater groups (P<0.05). The daily reduction of total phosphorus was not significantly different among the 3 fresh water groups and among the 3 seawater groups (P>0.05). The device has such characteristics as strong ability of reducing ammonia nitrogen and phosphorus, simple operation method and low operating cost, and can be promoted and used in aquaculture water purification.