[Purposes] To study the dynamic mechanical properties of marine soft soil-polypropylene fibre concrete composite layer under impact loading.[Methods] The dynamic compressive properties of polypropylene fibre concrete (PPRC) and marine soft soil-polypropylene fibre concrete composite layer (S-PPRC) specimens were tested using a split Hopkinson pressure bar (SHPB) and the results of the tests for each type of specimen were comparatively analysed.[Findings] The results show that the dynamic compressive strength of PPRC specimens is significantly higher than the static compressive strength, more sensitive to the loading rate, and suitable for high strain rate environment, the dynamic compressive strength of the specimen doped with 1.25% grows the fastest; the damage characteristics of the S-PPRC composite layer specimens with the increase of the strain rate are mainly divided into three types, i.e., interfacial shear damage, the dynamic crushing of the concrete layer, and the debris morphology; the composite layer specimens exhibit obvious nonlinear behaviour and the characteristic that energy is mainly reflected, in which the fibre doping 1.25% specimen has the greatest dynamic strength compared with other specimens, which is more suitable for loading under high strain rate conditions, the impact toughness curve shows a straight line increase, and the dynamic elastic modulus grows by 347.18% with the increase of strain rate, in addition, its absorption and transmission energies grow the fastest, and the maximum is under the loading of high strain rate conditions, while the absorption capacity continued to increase with the increase of strain rate and resisted the impact better. [Conclusions] The dynamic mechanical properties of S-PPRC composite layers can provide a research basis for fibre concrete supported coastal tunnels.