In view of the abnormal quality of circulating water system in the ammonia synthesis unit and alkylation unit of Hebei Jiheng Group Corporation Ltd.,  the composition of slow-release and scale-inhibition for circulating water was analyzed, and the mechanism of slow-release and scale inhibition was discussed. The analysis data show that the leakage of heat exchanger is the main cause of water quality deterioration, at the same time, the countermeasures are found out and good results are achieved.