For lasers which are working in the changing state all the time, the process of single particle radiation on semiconductor laser is analysed, and space radiation effect is described as the cumulation of radiation effects caused by single particles. In consideration of the characteristic that the arrival of particles is a Poisson process, the performance degradation model of space irradiated semiconductor laser is established. Expressions of reliability and mean time to failure are educed. The performance degradation process of multi-quantum well semicondyctor laser in high-orbit space radiation environment is simulated using existing data, and curves of degradated optical power are obtained. Results show that degradated optical power is in direct proportion to radiating time. Therefore, taking into account of both radiation effects and annealing effect, the degenerate rate of optical power is put forward, which is in direct proportional to the average radiating dose of space radiation environment calculated by fitting. Reliability curves are achieved and the mean time to failure for device is calculated.