This present study investigates the dynamic response of reinforced concrete tunnels subjected to internal explosion using three dimensional explicit Finite Element analyses. The analysis is carried out using the Finite element tool Abaqus/Explicit. A typical underground tunnel of 5 m diameter embedded in a clayey stratum at a depth of 9.0 m below the ground level is considered for the analysis. Lagrangian elements were used to model the soil and concrete lining. Soil is modelled using Drucker-Prager elasto plastic model. Lining is modelled using concrete damage plasticity model. CONWEP blast load is applied to the lining surface as a triangular impulse. The influence of charge weight on the lining response is investigated here. The lining displacement becomes less significant at a distance of 1.5 times the internal diameter of the tunnel from the blast source. The displacement of the soil near the ground surface increases from 1 mm to 10 mm for the explosion of 10kg to 75kg TNT.