The rock-anchored crane beam of an underground plant is calculated by the method of secondly-divided grid and 3-D elastic-plastic nonlinear FEM. On the basis of the initial stress field, the global model of under-ground plant was used to calculate stage excavation and the field stress after excavation was got. Then this stress field is used to interpolate calculation and the initial stresses of crane-beam model are obtained. On this base, the crane-beam model under loading is calculated and different crane-beam shapes of normal-excavation, over-excavation, and under-excavation are studied. Their stress characteristics, stabilities and the anchor bars stress states are roundly analyzed and the disadvantages of excessive and insufficient excavation are definitely indicated. Moreover, the influence of C and φon the safety factor is studied.