Abstract: Grain traits is an important factor affecting maize yield，and this experiment mainly analyzed the genetic characteristics and heterosis of the 57 sweet corn inbred lines and equipping 40 testcross combinations of hybrid seed grain traits. The results showed that there were significant differences in the performance of heterosis in grain traits. The heritability rate of over mid-parent heterosis was as high as 57. 50% in grain width，and 37. 5% in heterobeltiosis. The heritability rate of over mid-parent heterosis was 50% in grain length， and 30% in heterobeltiosis. The heritability rate of over mid-parent heterosis and heterobeltiosis were both 25% in grain thickness. The heterosis was as follows： grain width > grain length > grain thickness；F1 seeds were closely related to heredity when there was no significant difference in grain traits between parents. Therefore，to obtain a high yield by improving grain traits，it is possible to select parents with distant phylogenetic relationships for crossbreeding.

Key words: heterosis, grain trait, sweet corn