Abstract: The balance state of natural geostress will be damaged and stress will be redistributed during tunnelling, which will cause cracking, developing and cutting through of fissure under the effect of tectonic stress field or selfweight stress field, then tunnel collapse and instability will happen. A contrastive analysis was conducted regarding the effects of crack location, length, depth etc. on the stability of surrounding rocks of a horseshoe-shaped tunnel by numerical simulation and laboratory model test. As for the numerical analysis, it analyzed the failure modes of surrounding rocks and calculated the stress intensity factor of crack tip. As for the model test, the effect of cracks on compressive strength of tunnel model was studied. The research shows that: (1) the results of numerical simulation mainly agree with that of the model test; (2) the maximum effect on tunnel stability is those cracks at the corner of tunnel or at tunnel roof with 45° inclination; (3) the longer of a crack in tunnel is, the lower the compressive strength of tunnel model is; (4) as crack length reaches a certain value, the effect of crack depth on tunnel stability increases linearly; (5) the stress redistribution and failure patterns of surrounding rock mass are much effected by tunnel cracks.