The invention discloses surface treated calcium carbonate powder and a preparation method thereof. The surface treated calcium carbonate powder is prepared from the following raw materials of broken calcium carbonate, a grinding aid, sodium dodecyl sulfate, aluminum acetylacetonate, magnesium oxide, diethylene triamine sodium pentacarboxylate, a modifier, 3-aminopropyltriethoxysilane, phthalandione bis(2-ethyl hexoate) ester, modified polyacrylate, hexenyl distearamide, 2-(2'-hydroxyl-3',5'-ditert phenyl)-5-benzotriazole chloride, polyacrylamide and a stabilizer. The surface treated calcium carbonate powder is prepared by the steps of stone cleaning, removing impurities, dewatering, breaking, grinding, surface modifying, performance adjusting, smashing, drying and the like. The surface treated calcium carbonate powder disclosed by the invention can be fully dispersed, has small agglomeration after being added into plastic and has good dispersity, and all items of mechanical property of modified calcium carbonate are all remarkably improved.