The levels of damage caused by the mirid bug Apolygus lucorum Meyer-Dür on fourteen cotton varieties during the growing season were investigated in the field. Of these varieties it was found that Yazhoumian displayed the highest resistance to A. lucorum, that twelve cotton varieties including Jifengza-7 displayed moderate resistance, and that Ling\|17 appeared the most susceptible. The reflectance from the canopies of the 14 varieties was measured by ASD Handheld Spectroradiometers and correlation analysis was undertaken to determine the wavebands that were sensitive to damage levels. The first derivative values of canopy reflectance were found to differ significantly among varieties from 690 to 750 nm (P <0.05). Also, the first derivative value of canopy reflectance at 717 nm showed a significant negative correlation with the index of resistance to A. lucorum for cotton plants at the seedling stage (P <0.05), which could reflect the levels of damage caused by A. lucorum. Therefore, spectral models based on reflectance from the canopy could be used to diagnose the resistance of cotton plants to A. lucorum.