A mannuronic dicarboxylic acid oligosaccharide composition, which comprises mannuronic dicarboxylic acid of formula (III) or a pharmaceutically acceptable salt thereof, where n is an integer selected from 1-9, M is selected from 0, 1, or 2, m' is selected from 0 or 1, the total weight of mannuronic dicarboxylic acid for which n = 1-5 accounts for 80-95 pcnt of the total weight of the composition, and the ratio of the total weight of mannuronic dicarboxylic acid for which n = 1-3 to the total weight of mannuronic dicarboxylic acid for which N = 4-7 is between 1.0 and 3.5.
