This study investigates the photogenerated carrier dynamics in gallium antimonide (GaSb) crystals using reflective optical pumping-terahertz detection technology. First, we examined fluctuations in terahertz time-domain peak intensity caused by varying the energy density pump light at a wavelength of 400 nm. Based on results of this examination, we derived the recombination time of photogenerated carriers in GaSb crystal. Next, we recorded the terahertz time-domain spectrum of GaSb crystals under different energy-density pump light conditions at a wavelength of 400 nm. This helped in calculating the GaSb conductivity in the terahertz frequency band. Finally, by leveraging the Drude-Smith model, we conducted conductivity fitting and extracted key parameters, including the Smith parameter and carrier scattering time. This study provides valuable insights into GaSb material modification and related detector manufacturing.