The invention relates to a GC-IRMS direct measurement method for hydrogen sulfide sulfur isotope in mixed gas, which comprises the steps of: firstly, by utilizing a gas chromatogram-stable isotope ratio mass spectrum combined instrument with I s o d a t N T 2.0 software, carrying out the magnetic field control so that an intermediate receiving cup receives ions with the receiving charge-to-mass ratio of 35, which are 35H2S, and correspondingly, receiving cups on two sides respectively receive ions with charge-to-mass ratios of 34 and 36, which are 34H2S and 36H2S, and recording a numerical value of a magnetic filed at the moment; then correcting the instrument by H2S reference gas; secondly, injecting a plurality of gas samples containing 1-5ml H2S into a gas chromatograph in the instrument, and meanwhile obtaining gas chromatograms of 36H2S, 35H2S and 34H2S and gas chromatograms of ratios of 36H2S/34H2S and 35H2S/34H2S; finally, processing obtained data to gain a value of hydrogen sulfide sulfur isotope in a mixed gas sample. The GC-IRMS direct measurement method has the characteristics of simpleness, rapidness, accuracy and small sample consumption, and does not need sample preparation and correction of interference isotopes.