The study analyzed the optical response of GaAs0.75Sb0.25 nanosheet under high pressure. It is the generalized gradient approximation (GGA) within the framework of density functional theory (DFT) was employed by means of a simulation program, which is called CASTEP. Under different pressure (P = 0, 2, and 4 GPa). Geometry optimized parameters were calculated for the nanosheet. The optical data alter in accordance with high pressure. The increase of pressure in the nanosheet led to a rise in p = 4 GPa and a decline in p = 2 GPa of the optical energy band gap, the static dielectric constant 𝜀1(0), and optical conductivity. The discussions of the real 𝜀1(𝜔) and imaginary 𝜀2(𝜔) sections of the dielectric function, optical band gap energy, optical absorption, and optical conductivity were included.