To assure the pointing accuracy in a shooting target to be better than 30 μm for the Shen Guang Ⅲ(SGⅢ)facility,the switchyard of target area for the facility was designed and the rigid frame and transport mirrors in the switchyard were optimized to improve their stability. In design, the reinforced concrete was used to support the switchyard, and the tilted supports were added in the steel frame of switchyard to decrease and distribute the mass load reasonably.Furthermore, the herringbone supports were firmed to local horizontal beams. The transport mirror supports were also designed, in which their foundational frequencies were much higher than that of the swichyard. By above ways, the angle shifts of transmission mirrors in random broadband vibration can be suppressed successfully. The mechanical analysis of range structure by Finite Element Analysis(FEA) indicates that 87% of transport mirrors show their angle shifts less than 0.48 μrad. According to the relation between the rotation drifts of the optics components and the positioning errors of optical path, it can be seen that the rotation drifts of the transmission mirrors could meet the stability requirements for the positioning error of each single optical path not more than 12.9 μm.