In this paper, in order to study the change of φ(CO)/φ(CO₂) with temperature in the process of low temperature oxidation in Yima gas coal mined-out area,a constant temperature heating device designed by ourselves was applied to carry out isothermal oxidation of the prepared mixed grain size coal sample at different temperatures. Then by analyzing the produced gases with GC-950 gas chromatograph, the concentration of CO and CO₂at different temperature and time was measured, and the φ(CO)/φ(CO₂) values were calculated. By analyzing the relationship between φ(CO)/φ(CO₂) value and time at different temperatures ,it is concluded that the φ(CO)/φ(CO₂) value tends to be a stable value when the oxidation reaction is carried out for a period of time, and the higher the temperature is, the shorter the time will be. Then the relationship between the stable value of φ(CO)/φ(CO₂) and the temperature was analyzed, and the linear relationship between φ(CO)/φ(CO₂) value and temperature was verified by fitting analysis, which is of great significance to the production. By comparing the superiority of φ(CO)/φ(CO₂) value and φ(CO) value as an index value, it is concluded that φ(CO)/φ(CO₂) value is of more superiority than φ(CO) value in Yima gas coal mined-out area.