In order to define the geochemical characteristics and cause of formation for the rock salt in the Majiagou Formation, east part of Ordos Basin, C, O, and Sr isotopes and trace elements of carbonate rocks are analyzed and studied. The results show that δ13C concentration is between -3.46‰ and 1.08‰, isotope ratios of Sr are significantly low, the ratio between Sr and Ba is generally bigger than one, LREE is enriched more than HREE, Ce has a weak positive anomaly, Eu has an obvious negative anomaly, and the ratio between V and (V+Ni) is between 0.7 and 0.8. Experimental results indicate that since the climate is dry and hot, the water is deep, and the depositional environment is reductive and marine, the depositional process of rock salt is affected by mantle derived materials.