We investigated the removal of organic matters with different molecular weight (MW) and HAAs formation potential composed of organic matters with different MW in the two processes of 03/BAC and micro-aeration/BAC, and discussed the characteristic of forming HAAs by organic matters with different MW. The results indicated that more than 90% of organic matters with >30 x 10(3) molecular weight could be removed in the process of O3/BAC. In the water treated by the two processes of O3/BAC and micro-aeration/BAC, the percentage of organic matters with < 10(3) MW exceeded 50%, 10 x 10(3)-30 x 10(3) MW was in 20%-30% based on UV254 value as token of organic matters. And the HAAs generated by the organic matters with < 10(3) MW occupied the main fraction, and the concentration of DCAA, TCAA and DBAA in the tow processes was 97.00, 38.55, 2.10 microg/L and 104.00, 42.75, 2.92 microg/L. Finally, preferable linear relationship were found between UV254 and HAAs formation potential in finished water of the process of O3/BAC, because of the better linear fitting correction coefficient between UV254 and DCAA, TCAA, DBAA and THAAs, that is 0.827, 0.8513, 0.8157 and 0.878.