Abstract: Stalagmites can rebuild the paleo-climate of decades and hundred years, which need more accurate detection of trace carbonates in order to achieve high spatial resolution. However, the traditional phosphate acid method with weight about 10 mg has been unable to meet analysis of trace samples, and the laser microprobe mass spectrometry method requires calibration for test results. Carbon and oxygen isotopes of trace carbonate samples have been detected by using Kiel Ⅳ-IRMS with on-line dual technique. Different carbonate standard reference materials of GBW 04405 and NBS 19 were detected under different reaction times and different weights, and the test results were compared with Gasbench Ⅱ-IRMS results. The results indicate that isotopic fractionation values of different carbonate standard reference materials are different, caused by different reaction times. 55 carbonate standard material of GBW 04405 with weight about 4-85 μg have been analyzed and mean values of δ¹³C and δ¹⁸O are 0.574‰±0.027‰ and -8.519‰±0.065‰ which are consistent with certified values of 0.57‰±0.03‰ and -8.49‰±0.14‰, respectively. 14 carbonate standard material of GBW 04405 have been analyzed by Kiel Ⅳ-IRMS and GasbenchⅡ-IRMS with weight respectively about 50 μg and 140 μg. The results of δ¹³C and δ¹⁸O are 0.576‰±0.012‰ and -8.501‰±0.050‰ detected by Kiel Ⅳ-IRMS, 0.569‰±0.034‰ and -8.590‰±0.099‰ detected by Gasbench Ⅱ-IRMS. The test result of the on-line dual technique consumed less sample, had better precision and were more reproducible than that by GasbenchⅡ-IRMS. The method of the on-line dual technique meets the requirements of trace carbonate detection and carbonate sample applications can be used to achieve high spatial resolution.