The explosion venting is an effective way to reduce hydrogen-air explosion hazards, but the explosion venting has been less touched in an obstructed container. The present study mainly focused on the effects of hydrogen concentration and film thickness on the explosion venting in a small obstructed rectangular container. High speed schlieren photography was employed to obtain the flame fine structure and velocity. Pressure transducers were used to measure the overpressure nearby the obstacle. The experimental results show that the obstacle has a significant effect on the flame shape, tip speed and overpressure. In the process of flame evolution, the flame surface becomes more wrinkled with time after the tulip flame. Compared with the cases without the obstacle, the flame surface becomes more distorted and wrinkled downstream of the obstacle under the influence of obstacle enhanced turbulence and flow instability. Upstream of the obstacle, the lower part of the flame surface becomes concave while the upper part shows convex. The pressure histories show that the maximum overpressure increases with the hydrogen concentration in the range of 11.8%-23.7%. Two main pressure peaks were observed for all hydrogen concentrations in the presence of the obstacle. The Helmholtz oscillations appear after the second pressure peak and its duration increases slightly when the hydrogen concentration increases. The combined effect of the obstacle and hydrogen concentration on the second peak overpressure is more significant than on the first peak overpressure. Moreover, the maximum overpressure shows a monotonic increase with the film thickness. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.