Early prediction is one of the key technologies to the prevention and extinguishment of spontaneous combustion of coal. The aim of this study was to propose a type of scientific and convenient forecasting indicator for initial spontaneous combustion of coal in the gob area. The authors developed the calculation model of carbon monoxide (CO) concentration in the air return corner based on the generation mechanism, sources, and influencing factors of CO. The parameters obtained from both large-scale coal self-heating experiment and in-situ observation of four collieries in Yuanyang lake mine area were used to calculate the extreme value of CO concentrations on various stages of spontaneous combustion. The established indicators were applied to specific coal mine scenarios and combined with the in-situ measurements. It demonstrates that this method has provided the scientific guidance for safer exploitation on coal mines. Furthermore, the main reasons of unstable CO concentrations in the return corner and its relationship with prevention measures were also examined. In summary, the results showed that the forecasting indicators established can meet the requirements of identification of spontaneous combustion potential of coal in Yuanyang lake mine area.