Abstract: The distribution of oxygen concenlration and the velocity of air flow in a mined-out area were determined by numerically simulating the flow field. With the simulated results together with the duration and threshold of coal spontaneous combustion obtained from experiments, the spontaneous combustion dangerous zone was partitioned into three zones, and the smallest working face moving velocity to prevent spontaneous combustion was calculated. Compared with the simulation of the whole process of coal spontaneous combustion in a mined-out area, this proposed method requires a smaller amount of calculations, but its precision can satisfy the demand to predict and prevent spontaneous combustion in the mined-out area.