The　startup　operation　and　process　control　of　a　two-stage　sequencing　batch　reactor　(TSSBR)　was　investigated　to　improve　the　efficiencies　of　organic　substrate　degradation　and　nitrification　via　nitrite　from　a　chemical　industrial　wastewater　with　high　COD　and　nitrogen　concentrations.　A　control　strategy　using　process　variables　as　dissolved　oxygen　(DO),　oxidation-reduction　potential　(ORP)　and　pH　was　implemented.　The　conventional　SBR　test　results　showed　that　based　on　DO　and　pH　breakpoints　at　the　transition　of　COD　removal　and　nitrification,　organic　substrate　degradation　and　nitrification　could　be　separated　and　occurred　in　two　different　reactors　termed　TSSBR.　For　the　purpose　of　improving　the　process　flexibility　and　saving　aeration　energy,　the　variations　of　DO,　ORP　and　pH　in　TSSBR　were　characterized.　The　developed　control　strategy　for　TSSBR　was　that　in　the　SBR1,　DO　and　ORP　breakpoints　indicated　the　end　of　COD　removal;　in　the　SBR2,　the　DO　breakpoint　and　ammonia　valley　on　the　pH　profile　represented　the　end　of　nitrification;　a　nitrate　knee　on　the　ORP　profile　and　a　nitrate　apex　on　the　pH　profile　indicated　the　completion　of　denitrification.　A　stable　nitrite-type　nitrification　was　achieved　in　the　SBR2　with　nitrite　accumulation　rate　above　95%.　The　TSSBR　demonstrated　an　improved　organic　substrate　degradation　rate　by　40%　and　nitrification　rate　by　60%　in　comparison　with　conventional　SBR.　The　TSSBR　consisting　of　SBR1　and　SBR2　was　a　two-sludge　system,　i.e.,　heterotrophs　and　autotrophic　nitrifters　in　the　different　reactors,　which　is　favorable　to　improve　the　treatment　efficiency　and　increase　the　proportion　of　nitrifiers　in　the　SBR2　biomass.