Abstract: In this paper,the writer makes an engineering geological investigation on 29 survey lines which are decorated at ore drifts、transverse drifts or mining tunnels of 300m、360m、390m、420m、460 mand 500min an iron ore,and finds that there being 2groups of main joints by statistics,the trend of dominant structural plane being SE,about 80%joint angle ranging between 50～90°,and most direction of them being consistent with vein.Evaluating rock mass by Rock Mass Rating Classification method,we find rock mass quality classification of limestone、quartzite and sandstone all belong to 3rd category;And modeling and analyzing tunnel and dominant structural plane by Flac^3D,we know that the main factor of tunnel being unstable is that it is parallel with structural plane which has a guiding role for subsequent tunnel design.