The influence of different ignition positions and hydrogen volume fractions on the explosion characteristics of syngas is studied in a rectangular half-open tube. Three ignition positions were set at the axis of the tube, which are 0 mm, 600 mm and 1100 mm away from the closed end, respectively. A range of hydrogen volume fraction (phi) from 10% to 90% were concerned. Experimental results show that different ignition positions and hydrogen volume fraction have important influence on flame propagation structure. When ignited at 600 mm from the closed end on the tube axis, distorted tulip flame forms when flame propagates to the closed end. The formations of the tulip flame and the distorted tulip flame are accompanied by a change in the direction of the flame front propagation. The flame propagation structure and pressure are largely affected by the ignition position and the hydrogen volume fraction. At the same ignition position, flame propagation speed increases with the growing of hydrogen volume fraction. And the pressure oscillates more severe as the ignition location is closer to the open end. And pressure oscillations bring two different forms. The first form is that the pressure has a periodic oscillation. The amplitude of the pressure oscillation gradually increases. It takes several cycles from the start of the oscillation to the peak. For the second form, the pressure reaches the peak of the oscillation in the first cycle of the start to the oscillation. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.