Abstract: Based on investigating the characteristics of reflection spectrum of cotton canopy in different cotton varieties, irrigation and nitrogen levels，the results showed that there was a marked difference in the reflection spectrum of the canopy at different growth stages of cotton. The reflection spectrum of the canopy increased before flower and boll stage, decreased after flower and boll stage with the growth of cotton. The reflection spectrum of the canopy decreased in the near infrared region（700-800nm） and increased in the visible region（400-700nm） with increasing the irrigation level. There were some differences in the reflection spectrum of the canopy for different cotton varieties. The reflection spectrum of the canopy for the treatments of N1（135kg·ha-1nitrogen）and N3（540kg·ha-1 nitrogen） had a marked difference in the near infrared wave bands.

Key words: Cotton, Canopy, Hyper spectrum, Reflection rate