In this study, three different genotypes of purple corn (Zea may L.) including FHN, HN631 and JN20 were used to study the changes in seed coat color and the correlation between seed coat color (R, G and B values) and anthocyanin content among different varieties during grain filling period. The dynamic accumulation of anthocyanins and main nutrients in grains at grain filling stage was analyzed. The results showed that there was a significant negative correlation between RGB value and anthocyanin content (P < 0.05) in all the three varieties. Along with the grain development, the dynamic curves of anthocyanin, total soluble sugar and sucrose contents were similar, both increasing and then decreasing gradually. The contents of the total soluble sugar and sucrose reached the maximum at the 13^th day after pollination, while the anthocyanin content of grains reached the maximum at the 25^th day after pollination. The soluble protein content showed a decreasing trend, while amylopectin and amylose contents showed an increasing trend. The anthocyanin content was negatively correlated with the total soluble sugar, sucrose and soluble protein contents (P < 0.05), while it was positively correlated with the starch content (P < 0.05). In conclusion, RGB value can be used as an effective indicator for detecting anthocyanin content, 21-25 days after pollination can be used as the optimum harvest time of purple corn.