An integrated fixed-film activated sludge system (IFAS) was used to treat simulated wastewater with high-strength ammonia and organics in this study. The shortcut nitrification and denitrification coupled with anammox was successfully achieved after 83d operation through stepwise increase of influent ammonia nitrogen concentration (50~300mg/L) and low oxygen control (DO: 0.15mg/L). With the increase of ammonia nitrogen concentration, effluent nitrite accumulated significantly. When the influent ammonia nitrogen concentration increased to 300mg/L, the removal efficiencies of COD, NH₄⁺-N and TN reached 95.3%, 100% and 93.1%, respectively, and the total nitrogen removal loading rate (NRR) reached 0.14kg/(m³·d). The microbial activity test showed that the anammox activity was higher in the biofilm phase, while ammonia aerobic oxidation activity was higher in the sludge phase. With the increase of ammonia nitrogen and COD concentrations, extracellular polymeric substance (EPS) secretion and protein/polysaccharide (PN/PS) increased, promoting stronger impact load resistance and biological stability of the system. Microbial community results found that heterotrophic nitrification and aerobic denitrifier (Acinetobacter), anammox bacteria (Candidatus Brocadia and Candidatus Jettenia) were mainly enriched in biofilm, while partial nitrification bacteria (Nitrosomonas) was distributed in sludge. The sludge-biofilm separation mode facilitates directed proliferation of different nitrogen-removing bacteria. Functional gene annotation (KEGG) suggests that collaborative nitrogen removal in the IFAS system is via heterotrophic nitrification/aerobic denitrification and partial nitrification denitrification/anammox.