In　wastewater　treatment　process　(WWTP),　which　has　nonlinear　and　dynamic　characteristics,　it　is　difficult　to　realize　the　tracking　control　of　dissolved　oxygen　(DO).　To　solve　this　problem,　the　online　double　heuristic　programming　(DHP)　controller　based　on　leaky　echo　state　network　(LESN)　is　proposed,　the　controller　is　named　as　DHP-LESN　for　short.　Firstly,　three　Leaky　ESNs　are　used　in　DHP　to　produce　the　control　strategy,　the　system　state　and　the　derivatives　of　evaluation　function,　respectively.　Then,　the　online　gradient　algorithm　is　used　to　update　the　output　weights　of　three　LESNs.　Finally,　the　performance　of　the　proposed　DHP-LESN　controller　is　tested　and　evaluated　on　Benchmark　Simulation　Model　1　(BSM1).　The　simulation　results　show　that　the　proposed　DHP-LESN　controller　can　achieve　better　control　performance　than　PID　controller.　©　2022　IEEE.