In order to study the influence of mechanical changes of surrounding rock on coalmined areas, Flac 3D is used to simulate different phases of tunnel construction and demonstrate the mechanical variation of surrounding rocks and stress characteristics of support structures. The following results can be concluded that: (1) Grouting reinforcement with leading conduit can prevent surrounding rock deformation when the tunnel constructs underlying coal minedout area. (2) Primary support structure bears most of the surrounding rock stress after removing center diaphragms, and the minimal principle stresses at hance and arch foot section increase 13% and 41.3% respectively, which improves the stress condition of tunnel structure. (3) The bolted in minedout area can provide maximum axial force 226 kN, which anchors effectively. (4) When the coal minedout area underlies the construction tunnel, the method of rock filling and grouting helps to reduce displancement by proportion of 154.3%. Besides, the application of secondary lining structure improves the safety of tunnel construction.