In this study, a global activated sludge communities database was used to investigate the global distribution of filamentous bacteria. The dominant filamentous bacteria worldwide were Zoogloea ramigera and Eikelboom type 1863. The incidence of sludge bulking in samples from Europe (22.4%), South America (18.8%), and North America (15.6%) was significantly higher than in other continents. The distribution of remaining filamentous bacteria shows significant regional variability. In addition, climate significantly affects the distribution of filamentous bacterial populations. The filamentous bacterial abundance in samples from polar climates (7.36%) and cold climates (4.13%) was significantly higher than in other climates. Candidatus Microthrix parvicella and Tetrasphaera spp. were the dominant filamentous bacteria in cold region. Wastewater treatment processes are also key factors affecting filamentous bacterial populations. The incidence of sludge bulking (21.6%) and the average abundance of filamentous bacteria (5.08%) in samples from CM processes were the highest, mainly induced by Thiothrix spp. In addition, filamentous sludge bulking is easily induced by Thiothrix spp. in SBR processes, and sludge bulking is easily induced by Zoogloea ramigera in PFR processes. This study provides new insights into preventing and controlling filamentous sludge bulking globally.