The invention relates to a construction method for dam body seepage preventing curtain grouting and provides a construction method for the dam body seepage preventing curtain grouting. The grouting is carried out by a technology of dense holes, high pressure, fine cement wet grinding and concentrated slurry, and the seepage preventing ability, the corrosion resistance and the durability of a dam body curtain are improved; the seepage is prevented in a way of front blockage and rear discharge, the downstream seepage escapement point elevation of a dam body and the uplifting pressure in a dam are reduced, and the problems of frozen thawing and frozen expansion of concrete are solved. The construction method for the dam body seepage preventing curtain grouting comprises the following steps of: a. downwards drilling a group of curtain grouting holes at the top of the dam; b. drilling radial grouting holes on the upstream surface in a basic gallery; c. downwards drilling curtain connection grouting holes extending into a dam foundation in the basic gallery; d. carrying out grouting by high pressure, fine cement wet grinding and concentrated slurry; and e. drilling a water discharge structure which is communicated with the basic gallery in the dam body. The invention is mainly used for the seepage prevention and discharge reinforcement processing of the concrete dam.