The invention discloses a metakaolin-slag-based geological polymer used for cementing wells of oil fields and a high temperature retarder thereof. The high temperature retarder can effectively control the rate of setting of the metakaolin-slag-based geological polymer used for cementing wells of oil fields at high temperature. The high temperature retarder of the invention comprises the followingraw materials by weight percentage: A. at least an alkaline-earth metal salt of 80 percent to 90 percent; B. at least an inorganic sulfate of 10 percent to 20 percent.