Both alpha-PdBi2 and beta-PdBi2 are superconductors with topological nontrivial signs. Here we report that the alpha-PdBi2 superconductor is converted by pressure into the beta-phase superconducting polymorph, with the superconductivity being further enhanced upon decompression. Through high-pressure resistance and synchrotron x-ray-diffraction experiments, we show that the alpha phase transforms into the beta phase at P-c similar to 8 GPa, above which the superconductivity is robust up to the maximum pressure investigated in this work. More interestingly, when the applied pressure is gradually released from 42.9 down to 1.7 GPa, the T-c increases monotonously from 2.5 to 4.0 K. We argue that the observed unusual evolution of superconductivity can be explained by combination of pressure-manipulated crystal quality and the pressure dependence of T-c of the beta-PdBi2 superconductor.