The invention provides an analytical method for core remained salt isotope of formation water. The analytical method for the core remained salt isotope of the formation water comprises the following steps of: smashing a core fresh part; soaking the smashed core fresh part; carrying out secondary soaking on solid residues of the soaked core fresh part; and centrifuging and concentrating water separated out after the secondary soaking is carried out for a preset time, and testing various isotope ratios. The analytical method for the core remained salt isotope of the formation water solves the problems that the existing method is difficult and expensive, has poor accuracy and the like; and has the advantages that samples can be selected simply, the price is low, test data cannot be affected by other fluid media, and the accuracy of the isotope ratios of original formation water such as <87>Sr/<86>Sr, delta <37>C1, Cs2<11>BO2<+>/Cs2<10>BO2<+> and the like is improved.