The aim of this study is to investigate the response of metro tunnel systems subjected to internal blast loading using Explicit Finite Element analysis. Usually, these metro systems consist of two tunnels running parallel to each other. The recent terror strikes exposed the vulnerability of tunnels to explosion. In this study, a typical metro system with two tunnels of 5m diameter running parallel to each other is considered. The tunnels are embedded in clayey stratum with a burial depth of 9m below the ground surface. The tunnel-soil interaction was also considered in this numerical model. The effect of parameters like explosive quantity and tunnel spacing on the response of tunnels was investigated. The explosion tunnel yields for the explosive quantity greater than 50 kg of TNT. The influence of blast wave on the adjacent tunnel is less for the spacing greater than 2.2 times the internal diameter of the tunnel. © 2014 Korean Geotechnical Society.