The invention discloses a cycling treatment device for water of a fish tank. The cycling treatment device comprises a first microbe filter layer, a first air intake mechanism, a second microbial flora layer, a third microbial flora layer, a fourth microbial flora layer, a fifth microbial flora layer, a second air intake mechanism and a miniature water pump, which are sequentially communicated with the lower part of the fish tank. The wastewater in the fish tank is completely subjected to filtration, sterilization and disinfection and is supplemented with air by physical and biological methods; the wastewater in the fish tank can be recycled; and meanwhile, a retractable exchange door is arranged on each filter layer, so that each filter layer can be timely cleaned and supplemented to reach the targets of convenience and repeated utilization.