Abstract: By taking two cotton cultivars with different temperaturesensitivity (Sumian 15, temperaturesensitive cultivar and Kemian 1, temperatureinsensitive cultivar) as materials, an experiment with two  temperature regimes (high temperature: 34 ℃\[38/30 ℃\], HT and control: 26 ℃\[30/22 ℃\], CK) were set in climate chamber to study the change of key matters in different genotypes cotton in response to high temperature and their relationships with fiber quality. The results showed that as treated in the
34.0 ℃ hightemperature regime for 5 days at different DPA (days past anthesis), significant change in fiber quality was observed in the temperaturesensitive cultivar Sumian 15. The key time window for fiber length, fiber strength and Micronaire in response to the high temperature stress was from 0 to 18.3 DPA, 10.9 to 26.1 DPA, and 10.5 to 34.0 DPA, respectively. So, it could be concluded that the key time window of cotton fiber development in response to high temperature stress was around 11 to 18 DPA. After treated under high temperature stress at the key time window for 5 days, the content of sucrose decreased firstly then increased compared with that in the control, the content of callose increased and the content of cellulose decreased by 4.2% in maximum. The fiber length decreased (by 23.3% in maximum), fiber strength increased (by 4.3% in maximum), Micronaire decreased (by 10.5% in maximum), and the general fiber quality deteriorated. Similar changes and trends were also observed in the temperatureinsensitive cultivar Kemian 1 except that the variation degree was comparatively lower.