A numerical model allows analysis of optical gain according to the electronic properties of AGaN/GaN multiple quantum well laser diode (MQWLD) under hydrostatic pressure. Finite difference techniques are used to acquire energy eigenvalues and their corresponding eigenfunctions of AGaN/GaN MQWLD. The hole eigenstates are calculated via a 6  ×  6  k  .  p method under applied hydrostatic pressure. It was found that the depth of the quantum wells, bandgaps, band offset, electron, and hole density increased with the increase of hydrostatic pressure. The electron and hole wave functions will have less overlap, the amplitude of the optical gain increases, and heavy hole and light hole interband relaxation time, and their excitons binding energy decreases with increasing pressure. A change in pressure of up to 10 GPa caused the optical gain peaks of light and heavy holes to shift to a high photon energy of up to 120 meV and enhanced the optical gain up to 1.7  ×  10⁵  m^−  1.