Abstract: Based on Mohr-coulomb criterion，a theoretical computation model about loosing rock zone of tunnel surrounding rocks under different lateral pressure coefficients was set up.Combined with a practical project，the range of loosing rock zone of circular roadway surrounding rocks under different lateral pressure coefficients is solved and analyzed.And the range of loosing rock zone during excavation is calculated by adopting the numerical simulation method，and the result are compared with that of the theoretical computation.The results showed that First，the loosing rock zone of tunnel surface is circle while lateral pressure coefficient λ=1 and the radius of the loosing zone increase with ground stress increasing.Second，the range of loosing rock will vary with different lateral pressure coefficients.The loosing range of roof and floor surrounding rocks increase with λ increasing.But，the loosing range in side walls will decrease with λ increasing while λ<1.0,and increase with λ increasing while λ>1.0.Last，the distribution law of loosing rock zone by theoretical calculating is basically identical to that by the numerical simulation.

Key words: Ground stress, Loosing rock zone, Theoretical calculation, Numerical simulation