It is regarded as an environment friendly way to obtain aquatic products by realizing the re-use of aquaculture water and closed production in recirculating aquaculture systems. The biological conversion of nitrite nitrogen to nitrate nitrogen is called Nitrification, which is the most common way to control ammonia-nitrogen in the present recirculating aquaculture systems.  Fixed-film biological filter, as a common way to realize nitrification and a key unit in a recirculating aquaculture system, can provide attachment surfaces for nitrobacteria to form bio-films. It can be divided into several types according to the different ways of contact between the bio-film carrier and the water flow or the different positions where the bio-film carrier flows through the fixed-film biological filter in the water body. The paper reviewed several types of frequently-used fixed-film bio-filters in recirculating aquaculture systems including trickling bio-filter, submerged bio-filter, fluid bed bio-filter, moving bed bio-film reactor,etc. in which the advantages and disadvantages of them were analyzed and compared, and specific cases were taken to illustrate the designs of bio-filters, thus providing reference for the construction of circulating aquaculture systems.