Abstract: The law of fruit development and changes in contents of sugar and acid of four mid-maturity sand pears in protected cultivation was studied. It was showed that Akibae, Kousui and Xueqing all matured in the first ten days of July, among of them, Akibae matured at first and Wonwhang matured in the middle ten days of July. The dynamic changes of sugar of four mid-maturity cultivars basically accorded with each other; there was evident difference between the changes of the contents of total acid of Wonwhang and other three cultivars during fruit development. The ratio of sugar and acid of Kousui picked on June 27 was 77.96 and the biggest of the four cultivars. As a result, Wonwhang, Kousui and Akibae are good mid-maturity cultivars, fitting to be grown in greenhouse and may be extended and applied widely.