Dynamic parameters of biochemistry including the contents of soluble carbohydrate (SC), crude fat (CF), fatty acid (FA) and soluble protein (SP) in American seng (Panax quinquefolium L.) seed are reported in the present paper. When embryo ratio (ER) increased from 7.31 to 20.48%, the SC content decreased from 4.08 to 1.16%. After that, SC content changed little. The CF content decreased successively from 34.50 to 14.40% from the beginning to the end during the embryo afterripening. The changes of FA content did not correlate with that of ER and the changing range of SP content was not large during the seed stratification. All of these may provide some information for understanding the dormancy mechanisms of American seng seed.