The effects of various structure parameters such as graded potential, strain, quantum‐well size, barrier heights, and temperature on the optical gain of single quantum‐well lasers are studied for a potential solution to the problem of device optimization from the unified point of view with a rigorous model for gain. This study on the structure parameter dependence of the gain with the valence band mixing as well as intraband relaxation is new and presents a unified scheme for the optical gain control. Significant enhancement of gain in the graded quantum well as compared with that of the ordinary square quantum well is predicted. With the uniaxial stress, the TE mode gain is suppressed while the TM mode gain is enhanced due to the change of valence band structure. Calculated results show that the roles played by structure parameters such as well width, barrier heights, and temperature on the optical gain becomes of great importance for the device optimization.