Cumulative damage to the exposed spacecraft materials by the micro-debris on low earth orbit， where the debris is densely populated， is one of the crucial problems calling for due consideration in designing of spacecrafts. The flux of micro-debris encountered by a typical sun-synchronous vehicle was calculated， the associated hypervelocity impact simulation experiment was carried out， and the damage equation was established. Based on the flux result and the damage equation， the surface damage ratio of the solar cell due to micro-impacts was calculated， and the associated optical transmittance decrease of the cell was evaluated according to optical measurement and theoretical model. The result showed that the surface damage ratio of solar cell after 10 a cumulative micro-impacts reaches 0.61% on average， and up to 2.3% in the worst case. The optical transmittance decreases by 0.5% on average， and up to 1.5% in the worst case. In this paper， a quantitative method of evaluation for the issue of solar cells surface damage due to micro-impacts was demonstrated through a concrete example.