Abstract: 【Objective】 To analyze the effect of different low temperature stress on chlorophyll fluorescence characteristics of different cotton varieties at bud stage，explore the cold resistance response law of cotton at bud stage，and screen the indexes related to cold resistance of cotton at bud stage，so as to provide theoretical basis and technical guidance for identification of cold resistance resources and breeding of cold resistant cotton varieties. 【Methods】 Three low temperature gradients were set at bud stage：T₁（20℃/15℃，day/night），T₂（15℃/10℃），T₃ （10℃/5℃） and CK （28℃/20℃）. 【Result】 The chlorophyll fluorescence parameters Fv，Fm，Fv/ Fo，qP and SPAD decreased，while NPQ and F o increased under low temperature stress. However，Fv/Fm increased at low temperature above 20℃/15℃ and 15℃/10℃，and decreased at low temperature below 10℃/5℃ and 15℃/10℃. 【Conclusion】 The degree of low temperature stress can be judged by the fluorescence parameters such as Fm and Fo of cotton in bud stage.