Abstract: In this paper, the elemental analysis-stable isotope ratio mass spectrometer (EA-IRMS) is modified to testing different forms of sulfur isotope standard material and sample. A SO₂ gas trap tube is installed after chromatographic column to trap the SO₂ gas generated by redox reaction and the captured SO₂ can be used as reference gas several times, there is no need to introduce high-purity SO₂ gas externally, which reduces the damage to the instrument pipeline corrosion and laboratory environment. When the amount of barium sulfate is about 400 μg, SO₂ gas in the trap tube can provide at least 20 peak center focus. Modified EA-IRMS system testing sulfur isotope standard material (IAEA-SO-5, IAEA-S-2, IAEA-S-3, EMA-P1), when the sulfur element injection volume is 20 μg, the δ³⁴S value test accuracy achieve 0.2‰(n=3), 4 kinds of international standard material measured value and true value have a good correlation coefficient (R²=1), it indicates that the δ34S value of different compounds of sulfur can be mutual calibration, and the modified EA-IRMS can meet the accuracy requirement of the sulfur isotope test.