Abstract: The stable carbon isotope composition in plant is a powerful tool for studying on carbon cycle， biogeochemistry and paleoenvironment. Element analysis- isotope ratio mass spectrometry (EA-IRMS) technology is a simple and precise method for measuring stable carbon isotopic composition. EA-IRMS technology was applied to determine carbon isotope composition of sample from environmental and geological fields. The suitable conditions for plant samples measurement on experimental results were chiefly ascertained through comparisons. Moreover，stability and linearity of EA-IRMS system, accuracy and precision of measurement were discussed and analysed. The results show that the measurement precision of carbon isotopes can be less than ±0.2‰ and the deviation of the measurement value is 0.01‰ when 7×10^-8 kPa of the vacuum, Cr₂O₃/Co₃O₄ oxidation furnace, 90-100 mL•min^-1 of carrier-He flow rate, 80 kPa of Conflo-He pressure and 110 mL•min^-1 of oxygen injection.