Considering the premature and late harvesting time in walnut producing areas of Wensu County, Aksu, Xinjiang, the uneven quality of walnuts is caused. In this paper, the cracking rate of walnut green peel was taken as the standard to study different harvest periods and measure external quality and internal change of walnut varieties Wen 185 and Xinxin 2, for determining suitable harvest time of walnut under different cracking rates. Samples were taken every 5 days, Wen 185 was taken from August 16th to September 5th, 2020, Xinxin 2 was from September 15th to October 5th, 2020, and each sampling was based on cracking rate (Wen 185: 0%, 5%, 20%, 50%, 95%; Xinxin 2: 0%, 5%, 50%, 70%, 90%), and the three diameters of fresh fruit and dry fruit, fresh fruit weight, dry fruit weight, shell thickness, kernel rate, moisture content, black spot rate, the contents of fat, protein, total sugar, tannin and trace elements of the two samples were determined. The results showed with the harvest time delay, Wen 185’s and Xinxin 2’s three diameters of fresh fruit and dry fruit, fresh fruit weight, dry fruit weight and kernel rates all increased, while shell thickness, moisture contents and shell black spot rates decreased. The appearance quality of Wen 185 nuts reached a high level from August 31st to September 5th, while the appearance quality of Xinxin 2 reached a high level from September 30th to October 5th. With the harvest time delay, fat and protein contents of Wen185 increased, while tannin and total sugar contents decreased. On September 5th, they reached the higher levels. Mineral element contents such as P, Ca, Zn, Na, K and Fe was on an upward trend, Cu was descending, and the peaks were on September 5th. Fat content, protein content, mineral element content (except Cu) from Xinxin 2 were on the upward trend. The content of tannin and total sugar decreased, and the peak values were from September 25th to October 5th. Early harvesting of walnuts will significantly reduce the appearance and internal qualities of nuts. Therefore, when cracking rate of Wen 185 green fruit reached 50%-95%, from August 31st to September 5th, and Xinxin 2 green fruit reached 70%-90%, from September 30th to October 5th were the suitable harvest times for the two kinds of walnuts.
