Experiments were performed in a narrow duct to scrutinize the evolution of premixed stoichiometric hydrogen/air flame propagation at varied initial pressures. Besides the formation of the classic tulip flame, new stages of flame deformation have been observed using high speed Schlieren photography, e.g. elongated tulip flame and T-shape flame. With decreasing initial pressure, the flame propagation tends to be milder, but the classic tulip shape is of robust appearance at all conditions. The measured characteristic times of flame deformation were compared with the predictions of Bychkov's model. The pressure wave generated upon the flame-wall contact at very early stage does not trigger the classic tulip inversion, but will collide with the flame front modifying the tulip structure after reflection on the end wall. Thereafter, three different types of pressure dynamics are initiated depending on the initial pressure, P-0 >= 0.7 atm, 0.5 <= P-0 <= 0.7 atm, or P-0 <= 0.5 atm. The Rayleigh-Taylor instability primarily accounts for the flame deformation, whose amplitude growth rate, omega is periodic and determined mainly by the flame acceleration, g according to the linear theory. The measured pressure dynamics by sensor is a combined manifestation originating from the flame dynamics, flame-induced flow and pressure waves excited during combustion. (C) 2019 Elsevier Ltd. All rights reserved.