A theoretical model on accumulation of temperature and stress in a three-junction GaAs solar cell is proposed to analyze its damage characteristics while irradiated by a multipulse laser. The distribution and accumulation effect of temperature and stress with different pulse widths are calculated. Specifically, the influences of pulse energy and duty ratio on the accumulation effect are discussed. Results show that the accumulation is weakened as pulse energy and duty ratio decrease and differ with the different pulse widths. The accumulation rate of stress is more rapid than that of temperature under nanosecond laser irradiation. Furthermore, tensile stress damage is the main damage form under nanosecond laser irradiation, and melting damage will change to main damage from a millisecond laser.