According to the characteristics of the stope layout in stoping crown pillar in thick and large ore body using upward drift slice mining method,the stress states of overlying rockmass,Point pillar,intervening pillar and crown pillar and the mechanical relations among them are analyzed using rock fracture process analysis(RFPA) method,and a mathematic model of mechanical state of roof of drift stoping face is established,the influence of drift layout along the strike and being vertical to the strike on the stability of exposed roof of drift is calculated,the thicknesses of top-safeguarding ore layer of stoping drifts with different widths are calculated.The calculated results can provide theory basis for the arrangement of preparatory works and safety management.