A numerical simulation method is proposed to evaluate the underground tunnel safety against explosion in adjacent tunnels. The dynamic constitutive relation used for rock material in the present study consists of a continuum damage model with the damage scalar depending on an equivalent tensile strain, a modified piecewise linear Drucker-Prager strength model allowing for the material strength degradation with damage, and a modified linear equation of state. The numerical model is calibrated by simulation of independent field explosion tests. Parametric study regarding the effect of the adjacent tunnel distance on the dynamic responses of underground tunnel is carried out. Failure zone around the explosion tunnel, and stress, strain and velocity on the adjacent tunnel wall are calculated. Safe separation distance between the adjacent tunnels is predicted and compared with empirical result.