In this study, the photoionization cross sections of C⁵⁺, Al¹²⁺, and W⁷³⁺ ions in a Debye plasma environment are calculated in the dipole approximation. The main emphasis is placed on investigating the influence of relativistic effects on shape resonances, Cooper minima, and virtual state effects. The relativistic effects lead to fine-structure splittings, allowing the appearance of double-shape resonance peaks in the total cross-section. Because the width and energy position of resonance peak are affected by the near critical screening length, the increase of nuclear charge Z leads to the significant differences in the size, width, and position of the double-shape resonance peak. The energy position of Cooper minimum in the photoelectrons is related to the critical screening length corresponding to the final continuum state. Unlike the deeper minima observed in the total photoionization cross-sections for C⁵⁺ and Al¹²⁺ ions, for the higher nuclear charge of W⁷³⁺ ions, the significant fine-structure splitting arising from relativistic effects results in substantial differences in the positions of the Cooper minima in the partial cross-sections. Therefore, when superimposed on the total cross section, these minima appear shallower. The W⁷³⁺ ion has a higher nuclear charge, and the screening length related to the virtual state effect is completely different from that of C⁵⁺ ion and Al¹²⁺ ion. Moreover, for the same screening length, there is a significant difference in the virtual state enhancement amplitude between C⁵⁺ ion and Al¹²⁺ ion in the low energy region .