In this paper, to improve the problem of low hole injection efficiency in the active region of a deep-ultraviolet laser diode (DUV-LD), a hole reservoir layer (HRL) is introduced based on the conventional DUV-LD and the HRL is changed to a five-step HRL with a decreasing Al mole fraction from n-region to the p-region. The HRL is numerically examined using Crosslight's Lastip software, which revealed that the application of the structure can achieve a higher carrier radiation recombination rate and a lower threshold current. When a five-step HRL with decreasing Al mole fraction is located between the last quantum barrier layer of DUV-LD and the upper waveguide layer, the electron leakage is minimal and the device performance is significantly improved.