Based on construction practice of worldwide concrete dam heightening project, 4 key construction technologies of concrete gravity dam heightening project by the integral heightening mode on the existing dam by the down stream side and on the dam crest were systematically summarized. The 4 key technologies are concrete raw materials and mix proportion, jionting between new concrete and existing concrete, controlled demolition and transference of old structures, and resources temporal and spatrial allocation curing construction period, For each key construction technology, the construction technical difficulties, features and requirements were analyzed, and the technical measures and solving strategies were summarized to provide construction reference for the same type project in the future.