Abstract: Iodine in carbonate rocks is crucial for reconstructing the redox conditions of the ancient marine environment and tracing the sources of ore-forming fluids. However, it is difficult to determine the iodine in carbonate rocks due to the extremely low concentration (＜1μg/g) and the loss of iodine-relative volatile in conventional acid digestion. In this study, a NH₄HF₂ digestion method was developed to prevent the loss of iodine in carbonate rocks during sample preparation. The sector field ICP-MS with high sensitivity was selected for the determination of iodine mass fractions in carbonate rocks. As results shown, it took only 1-6h at 220℃ for the complete recovery of iodine in carbonate rock GBW07114. The optimized mass ratio of ammonium bifluoride to the sample is 2, which avioded the reducation of sensitivity of iodine due to the introduction of a large amount of fluoride ions into ICP during analyzing iodine in carbonate rocks. Moreover, ammonia dilution effectively eliminated the serious matrix effect induced by large amount of Ca and Mg. The developed method was successfully applied to determine I in ten Chinese carbonate rock reference materials. The measured value of iodine in GBW07114 was agreed with the certified value. Most of measured values in carbonate rock refence materials were agreed with their information values. The RSD values of analytical results was 3.3%-19.1%. There was a significant exponential correlation between the measured mass fraction and its RSD in these samples, which indicated the measurement uncertainty was mostly due to signal intensity of idoine. The high RSD values (15.0%-19.1%) of analytical results in GBW07128, GBW07130 and GBW07131 may be due to the heterogeneities of samples. The LOQ of iodine in this method was 0.013μg/g, which satisfied the requirement for the determination of low content ioidne in carbonate rocks.