Abstract: By taking cotton fiber in high yield cotton field of north Xinjiang as the object, the niche-fitness theory were introduced, through analysis the niche-fitness of cotton fiber in three mono-topping and multi-topping intercrop system treatment, the result showed, it is acceptable that evaluate cotton fiber quality by niche-fitness, the niche-fitness value of cotton fiber at the middle part of the cotton plant is the biggest that topping inJul.10th and Jul.25th in this three treatment, moreover, with the increase of topping times, compare with it’s top part of cotton plant, the niche-fitness of cotton fiber at the low part of cotton plant have a raise tendency, the niche-fitness value of top and low part of cotton plant in multi-topping treatment is bigger than what of mono-topping. The position of biggest niche-fitness value of cotton fiber, which is topped in June 25th in multi-topping treatment move up to top.