The biodegradability and speciation of organics were studied through long-term analysis of A2/O treatment. The majority of the organic matters were particle organics which accounted for 61% of the total organics. The proportions of rapidly degradable, slowly degradable and refractory organics were 15. 8% , 54. 2% and 30% respectively. Rapidly biodegradable organics were mainly dissolved organics while slowly biodegradable organics were particle organics. The variation of these two kinds of carbon sources was analyzed during the treatment process. It was noted that microbial hydrolysis fermentation took place in the anaerobic and anoxic tanks, which led to the transformation of slowly biodegradable organics and the anaerobic tank had the highest transformation rate. The transformation and utilization of rapidly/slowly biodegradable organics were analyzed through calculation. The results showed that the transformation efficiency of slowly biodegradable organics in the anaerobic and anoxic tanks in two hours was 33% and 20%, respectively. Furthermore, the amount and species of aliphatic acid increased in the anaerobic and anoxic tanks comparing with raw water.