Abstract: The maximum design depth of Dahe reservoir (the lower reservoir) dam concrete cutoff wall is 30 m long, the whole area is 20 700 m2. In this article the construction technology is introduced, especially on the aspects of platform, experimental drill holes, unit hole base rock appraisal, drilling, slot shape, clean holes out, wall body casting, quality check. By quality control on key procedures and key parts we ensure the whole wall in good quality.