Four　ammonia　oxidizing　bacteria　(AOB)　strains　were　isolated　successfully　using　selective　medium　from　a　lab-scale　Completely　Autotrophic　Nitrogen-removal　Over　Nitrite　(CANON)　reactor.　Morphology　of　strains　and　colony　was　observed　and　species　identification　based　on　amoA　gene　showed　the　four　strains　were　Nitrosococcus　and　Nitrosomonas　related　bacteria.　The　effective　isolation　of　AOB　from　CANON　process　provided　theoretical　basis　for　enrichment　culture,　immobilization　and　genetic　engineering　of　functional　microorganisms　in　further　study.