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• A bionic tunnel portal model was constructed based on the characteristics of shark gills. • The dependence of the micro-pressure wave on the opening ratio and oblique cutting angle of the bionic shark gill tunnel portal was elucidated. • The relationship between jet-stream energy and micro-pressure wave was studied. In this study, the bionic principle is used to relieve the micro-pressure waves (MPWs) at the tunnel exit. A bionic shark gill tunnel portal with holes was studied, and the effects of the opening ratios and oblique cutting angles of the bionic shark gill opening tunnel portal on the initial compression wave (ICW) and MPW induced by a high-speed train (HST) passing through the tunnel are examined. The results show that when the opening ratio of the bionic shark gill tunnel portal is 24%, the highest mitigation effect on the ICW pressure gradient and MPW is observed. In addition, the high-pressure region of the ICW in the tunnel decreased with increasing opening ratio. The greatest mitigation effect on the ICW pressure gradient and MPW is obtained for the oblique cutting angle of the bionic hole on the tunnel portal (with an opening ratio of 24%) of 16°, because the oblique cutting angle facilitates the expulsion of the jet-stream from the bionic hole at the tunnel portal. [ABSTRACT FROM AUTHOR]