Quantum well lasers are irradiated by electrons with a total fluence of 1 10-16 cm-2. The output power is reduced and the threshold current is increased under electron irradiation. The displacement damage effect on quantum well laser is analyzed theoretically and we deduce the relationship between the radiation induced output power and threshold current change and the electron fluence. The formula fits the experiment data very well, and can describe the change trend of the laser performance under electron irradiation, it can also predict the behavior of quantum well laser under radiation environment and is valuable for practical application.