Abstract: The extraordinary outburst of CO₂ gas, coal and rocks happened on May 24, 1978 in aojie oalfield. The isotope compositions of the outburst gas and the carbonates relating to CO₂ gas. The results arc as follows: The δ¹³C values of the CO₂ gas are -0.55-4.81‰; and that of ealcitc veins are -15.88-+5.94‰ which are tending to be heavier with the. decrease of depth. The δ¹³O alues PDB. the same below) of the calcite distributed from-8.07 to-20.4‰; The values of δ¹³C and δ¹³ O of parry iron are-1.96-+2.66‰ and -8.55-11.97‰ respectively; The average δ¹³C value of HCO₃ in the barnt rock water is 2.325‰, and based on it, the calculated δ¹³C value of the primary CO₂ dissolved a the wanter is about -6‰, but that of free CO₂ released the solution is about -7‰; The δ¹³C can onate precipi-laied fron, the burnt rock water are 3.89-4.63‰, heavier than those of the HCO₃ dissolved in water. The above results show that there are isotope fractionation of carbon in the processes of the disselving and degassing of CO₂ gas and the precipitating of the carbonate. As the variation of the δ¹³C values of the CO, in the coal measures of the field is broad (The lightest is -43.44‰, it is difficult to simply of CO gas with the carberrates in their isolopic compositions. The He/4 He value of the gas in the outburst spot is (3.8±0.5)×108, showing that the outburst gas is a sypteal crust source gas. So it is necessary to strengthen the studying in geology and geochemistry er the eoalfitld ill itself for searching into the concrete source of the outburst gas.