Terrorist actions and defacements have become one of the widest threaten for humans and structures. Underground tunnels can be used as shelters against blast, so it is very important to study their behavior under blast loads. The safety of tunnels is lean because of the lack of suitable ways to discover these events early. Techniques are essential to quantify the resistance of underground structures against blasts as a protection and to calculate the risks caused by the failure of their elements. The appropriate advanced methods could be experimental, numerical, or a mixture of both. The experimental work is limited because of the cost and complication, and so numerical analysis is suitable for blast study in addition to available experimental tests. The parameters affecting the safety of tunnels such as the weight of explosive, lining material and thickness, soil stiffness, burial depth, thickness co ver, shape of a tunnel, diameter of the tunnel, the standoff distance, the location of blast charge and also the effect of one tunnel to another in case of twin tunnel discussed by various researchers have been overviewed in the present work. The paper presents an overview of the effect of blast on tunnels for beginner researchers and structural engineers to understand such complex loading situation. New strategies which can be adapted to mitigate the effect of surface and internal blast loads on shallow and deep tunnels should be investigated. Studies should use numerical simulation of a tunnel buried in a saturated soil profile to imitate real -world conditions.