As an important enabling technology and means to realize the intellectualization of water plants, how digital twin can play a great role in the construction of smart water plants in combination with the needs of process control is an important technical problem that our practitioners in the water treatment industry need to focus on solving. This paper puts forward the technical architecture system of smart water plant based on "digital twin", lists the key technologies involved in "digital twin" in smart water plant, and illustrates the great application value and significance of "digital twin" technology in smart water plant combined with specific water plant cases.