Study on ground control and mined-out area treatment is described in the paper. In-situ observing method for ground control and calculation results with two/three dimensional finite-element method are presented. Based on field measurements and calculation results, ground control in Changpo Tin Mine are revealed. Scope of unstable rockmass, particularly seriously unstable areas which need precautionary measures, are determined and evaluated. Practicable scheme for treatment of mined-out areas is proposed.