Dynamic compression experiments were carried out on cubic PMMA specimens and two kinds of trapezoid PMMA specimens by changing the transmission bars to steel and aluminum bar with the Loading device of split Hopkinson pressure bar (SHPB). The compression process of PMMA specimens was recorded by high-speed photography, and the breakage process of PMMA specimens was analyzed based on the force displacement curves and high-speed images. The evolution of deformation and diffusion resistance of PMMA specimens under impact loading was discussed. The results show that the failure of the sample is mainly caused by the partial failure front at the contact end, and then the failure front propagates to the inside of the sample and leads to the breakage of the sample. The failure front of cubic samples is preferentially generated at the transmission end under low speed impact and generated at the incident end under the higher speed impact. After changing the shape of the specimen and material of the transmission bar, the relaxation phenomenon is obvious, and the failure front only occurs at the incident end. The compressive deformation of the trapezoid sample before breakage is non-uniform, and the stress and strain in the sample gradually decrease with the increase of the cross section, and show a linear diffusion distribution. The strain distribution and shear activation diffusion equation were used to obtain the generalized diffusion resistance distribution of the failure front. The generalized diffusion resistance increases first in front of the failure front and decreases after the failure front and the amplitude of the generalized diffusion resistance is related to the release of local strain energy.