The role of underground metro tunnels in a modern urban society is indispensable. Nowadays, these populous metro tunnel networks are becoming a prime target for terror strikes around the world. Considering these terror threats, it is crucial to study the vulnerability of tunnels when subjected to an internal explosion. This paper evaluates the vulnerability of underground metro tunnels exposed to an internal explosion using the explicit finite element (FE) method. The developed FE model has been validated with the field data reported in the literature for free-field blast wave propagation. Parametric studies were also carried out using the developed models to investigate the effect of lining material, lining thickness, lining shape, and type of surrounding of soil on the blast response of tunnels. A typical metro tunnel of 5.0 m internal diameter embedded at a depth of 9.0 m below the ground level is considered for the analysis. Numerical analysis shows that reinforced cement concrete (RCC) tunnels suffer severe damage when compared with the cast-iron tunnels. Box tunnels are extremely vulnerable to internal explosion when compared with circular and horseshoe tunnels. RCC tunnels embedded in medium dense sand are less vulnerable when compared with soft saturated clayey soil.