The rapid fuel-air mixing enhancement is one of the important issues for the efficient operation of scram-jet engines, and it attracts an increasing attention all over the world. The influence of jet-to-crossflow pressure ratio arrangement on the turbulent mixing in the staged transverse injection flow field has been investigated numerically, and the multiport injection system with four square-shaped portholes arranged in tandem has been employed as the simplest configuration in the current study. The numerical approach has been validated against the available experimental data in the open literature, and the predicted wall static pressure distributions show reasonable agreement with the experimental data for the cases with different jet-to-crossflow pressure ratios. The obtained results show that the larger jet-to-crossflow pressure ratio of the primary injector is beneficial to the mixing improvement irrespective of the arrangement of the other jet-to-crossflow pressure ratios, and the evolution of the vortex structure keeps nearly the same irrespective of the jet-to-crossflow pressure ratio of the primary injector. When the jet-to-crossflow pressure ratio of the injector 3 is larger than that of the injector 4, it is beneficial to the evolution of the vortex structure, and this would induce the mixing improvement, as well as the flame holding ability. The largest mixing efficiency is 73.6% at the cross-sectional plane x = 340 mm just downstream of the last injector in the range considered in this article. (c) 2014 Elsevier Ltd. All rights reserved.