The Guanjingang water plant has a capacity of 300,000 m3/d and is one of the main water plants of Jiaxing City in Zhejiang Province, which is located in the southern suburban area of this city. Its second phase with an augmentation of capacity of 150,000 m3/d was put into operation in September, 2012. The raw water for this plant is the surface water that purified by the artificial wetlands and goes through the combined treatment of a biological preprocess, with both conventional and advanced process, to ensure the water quality meets the standard. This paper mainly focuses on the three key problems: the seasonal high ammonia-nitrogen, biological security and pH control of outlet water. And it aims to optimize and analyze the combined processes including the artificial wetlands, biological pretreatment, sand filtration and advanced treatment with ozone-activated car-bon. Subsequently, the new treatment process applied to this practical engineering design is proposed.