Abstract：A simplified mechanical model of ultrahigh pillar with initial geometrical imperfections was established and the stability of the system was discussed by means of initial deflection function，the stress-strain relation of rock，the strain-curvature relation，static balance at elastic stage and at elastoplastic stage. The compliance relations between the stability of ultrahigh pillar and initial geometrical imperfections were established and ultimate load of ultrahigh pillar with initial geometrical imperfections were obtained at elastoplastic stage. The results show that the general deflection of ultrahigh pillar with initial geometrical imperfections is the product initial deflection function and under the load of upper rock mass at elastic stage；and the maximal deflection relates to initial deflection imperfections factor f0 and it increases with the increase of f0 before reaching critical state；and that the ultimate load of ultrahigh pillar decreases with the increase of initial deflection imperfections factor f0 at elastoplastic stage. Furthermore，an example was calculated based on Dongguashan copper mine；the estimated results correspond to practical experience so as to provide basis for mining order and arranging stope.
