Abstract: The damblocks of 15, 17 and 19 are the discharge orifice blocks, and cracks appeared before deep outlet base plate concrete pouring, especially the dam block 15 was worst. The No. 1 crack, 11- meter far way from upstream face and belowthe elevation of 347.5 was 11.5- meter deep. Cracks threatened the structural safety of cantilever beamand measures were took, such as prestressed cable, embedded anchor rod and chemical grouting. Jetting were found around the prestressed cable on the dam block 15 in the April 2007. Monitoring data showed that the cracks were changing slowly but the jetting was increasing. Quantitative analysis showed that the jetting was related to water level and time effect but not temperature. Jetting would shorten the life of cable, anchor rod and steel so that should be treated, to ensure the safety and durability of the dam.