In　wastewater　treatment　process　(WWTP),　it　is　very　challenging　to　realize　the　optimal　control　of　the　operation　variables,　since　the　process　contains　a　changing　number　of　objectives.　In　this　paper,　an　intelligent　optimal　control　with　flexible　objective　functions　(FOF-IOC)is　proposed　to　deal　with　the　optimal　control　problem　for　improving　the　operation　performance.　Compared　with　the　previous　optimal　control　methods,　this　proposed　FOF-IOC　has　three　main　advantages.　Firstly,　an　optimal　control　scheme　is　developed　to　describe　the　dynamics　of　the　operation　process.　In　this　scheme,　the　different　time-scale　operation　objectives　are　formulated　to　facilitate　the　optimal　control.　Secondly,　a　flexible　objective　functions　strategy　is　designed　for　determining　the　appropriate　objective　functions,　where　the　number　of　the　objectives　can　be　different　under　the　distinct　operation　time.　Thirdly,　a　dynamic　multiobjective　particle　swarm　optimization　(DMOPSO)algorithm　is　investigated　for　optimizing　the　flexible　objective　functions,　where　a　maximum　dimension　criterion　is　designed　to　cope　with　the　nouniform　optimization　dimension.　Finally,　the　proposed　FOF-IOC　is　tested　in　benchmark　simulation　model　No.1　(BSM1)to　evaluate　its　effectiveness.　The　results　demonstrate　that　the　proposed　FOF-IOC　can　achieve　satisfied　performance.　©　2018　IEEE.