Abstract: Ice wine belongs to the highest class of high-quality wines and is recognized as the best wine in the world. The quality of ice grapes plays a decisive role in the quality of ice wine, and the differences in climate conditions in different regions and interannual climate changes have a great impact on the quality of ice grapes. Different harvest dates after maturity correspond to different weather conditions and fruit quality. Therefore, it is particularly important to determine the harvest date of ice grapes. In order to determine the optimal delayed harvest date of ice grape in Yili River Valley, ice grapes from the observation area were harvested in stages from 2018 to 2019. This experiment was conducted in Yining County and the grape was harvested in different dates and then the contents of the total sugar, total acid, and sugar-acid ratio in grape fruits were measured in the laboratory thereafter. The correlation analysis, partial regression analysis and multiple linear regression analysis were applied to figure out the quality change rule, inter-annual quality change rule, and the relationship between quality and meteorological factors of ice grapes in different delayed harvest periods. Conclude the best harvest period when ice grapes reach the ‘best quality’ in Yili River Valley. Provide a reference for optimizing the quality of ice grapes and rationalizing regional management in the future. The results showed that:（1）the content of the total sugar and total acid in 2018 and 2019 had the same trend with the delay of the harvest date. The total sugar gradually increased with the delay of the harvest date, and the total acid climbing firstly and then fell down. （2）Average temperature of 120 days before harvest(T120), average minimum temperature of 120 days before harvest(Tmin120), average daily temperature range of 30 days before harvest(ΔT30) were the most important factors affected total sugar content of ice grape. Average temperature of 120 days before harvest(T120), average minimum temperature of 120 days before harvest(Tmin120), the average relative humidity of 120 days before harvest(RH120), and the average relative humidity of 60 days before harvest(RH60) were the most important factors affected total acid content of ice grapes. （3）7.5℃≤T120≤18.3℃, 4.8℃≤Tmin120≤9.6℃, 48%≤RH60≤70%, 52.3%≤RH120≤64.8% were the suitable range of meteorological conditions required to form the ‘best quality’. The best harvest date is reached when the current weather conditions meet the above range. The optimal harvest date of ice grapes in Yining County was November 21 in 2018, the optimal harvest date of ice grapes in Yining County was December 1 in 2019. According to the meteorological conditions, the optimal harvest date of ice grapes in Yining County in 2020 was verified. The results are consistent with the reality, indicating that the research results can be used for practical promotion.

Key words: Ice grape, Optimal harvest date, Regression analysis, Meteorological factors, Grape quality