The　biological　treatment　system　for　high-strength　wastewater,　particularly　landfill　leachate,　typically　requires　high　sludge　concentration　to　maintain　nitrogen　removal　performance.　However,　it　frequently　causes　an　excessive　accumulation　of　toxins　in　microbial　metabolism,　resulting　in　unstable　performance　during　long-term　operation.　An　efficient　two-stage　partial　nitrification/anammox　(PN/A)　mature　landfill　leachate　process　with　low　sludge　concentration　was　constructed　by　settling　time　reduction　and　Ca2+　addition.　The　ammonia　removal　rate　reached　46.7　mg　N/(L　center　dot　h)　in　PN-SBR.　Nitrosomonas　(2.0%)　was　the　sole　genus　responsible　for　partial　nitrification.　The　influent　NO2-N/NH4+-N　of　A-SBR　was　kept　at　1.39,　leading　to　a　dynamic　equilibrium　of　anammox　and　denitrification.　Ca.　Brocadia　recovered　fastest　(0.32%　-＞　1.8%)　among　the　detected　AnAOB　genera.　The　process　achieved　NRE　of　95.0%　with　effluent　TIN　of　37.6　mg/L　(＜40　mg/L).　This　research　offered　recommendations　for　the　favorable　operation　of　the　two-stage　PN/A　mature　landfill　leachate　treatment　system　with　low　sludge　concentration.