Abstract: Improving detection technique and level is the leading requirement of improving the hazard prevention effects of hydraulic engineering by applying new techniques and new methods. Take the seep disease prevention of one reservoir of Putian in Fujian for example, the seep position, burying depth and spatial distribution of the reservoir's dam were determined by electromagnetic wave absorbing CT detection technique,which. has provided the key basis for the stabilizing disposal of the seep hazard prevention of the dam and dam foundation, and a good effect has been got. It is a successful example of the application of the CT technique of electromagnetic wave in the hazard prevention of hydraulic engineering,which has provided experience and data accumulation for the further generalization and application of the CT technique of electromagnetic wave in engineering investigations.