In order to improve the accuracy of detection and assessment,we need to distinguish the type and cause of the crack in the detailed investigation of classifying assessment,and recognize the structural problems in the structures according to the cracks.Starting from common cracks in harbor hydraulic structures,we analyze the causes of the common cracks,discuss the crack limit standards and classifying standards,and expound the actual application of crack classification and assessment in hydraulic structures based on a real case of detection and assessment.