Optical gain and loss of microcavity greatly affect the quality of lasing, how to improve optical gain and decrease optical loss is of great significance for the preparation of laser. In this study, four types standard microdisks with different thicknesses of 2.2 μm, 1.9 μm, 1.7 μm, and 1.45 μm were fabricated by micromachining technology process to modulate optical gain and loss of microdisk lasing. The whispering gallery mode lasing in the ultraviolet range of GaN microdisk devices was investigated for these devices in order to clarify the effect of microdisk thickness on device characteristics. The quality factor Q and lasing mode number for different thicknesses are calculated from the stimulated spectra. The lifetimes of the exciton combination properties of the devices were observed using time-resolved PL spectroscopy. The lasing modes are modulated, and the lifetime decreases, while the Q factor of the devices first