Abstract: 【aim】To assess cotton delayed cool injury objectively, 【method】 The calculation method of heat index was designed to assess heat on the growth of cotton in this paper. Based on the average temperature of a period of ten days collected from nine representative stations located in three cotton regions in Kashi, Akesu and the north of Xinjiang，heat index were calculated at five growth stages and heat index at the beginning, middle, end and the whole growth stage were obtained. 【result】 Analysis showed that heat index could qualify for assessing heat not only at the whole cotton growth stage but also at every period of ten days, certain or several growth stages. As the index values have corresponded well with the year of yield reduction due to climate, it can be used as a reference of cotton production and distribution of types. Moreover, it could better reflect the occurrence status and extend of delayed cool injury in cotton. 【conclusion】Therefore, heat index is a proper index in assess ment of cool injury.

Key words: cotton, delayed cool injury, heat index, assessment