Abstract: Heritability and genetic correlations between 19 traits were estimated from data obtained from 6 Chinese Simmental farms using an animal model and MT-DFREML.Data relating to secondary traits and production traits in 1 634 Chinese Simmental cows were collected from 1980—2000.The traits analyzed were calving interval, open days, gestation length, milk yield, fat yield, protein yield, fat percentage, protein percentage, somatic cell score, milking speed, herd life, and linear type score (which included type score, rear leg view, fore udder attachment, rear udder width, rear udder height, teat placement, udder conformation, and udder vein). Estimated heritability of each trait were 0.08, 0.07, 0.08, 0.16, 0.15, 0.41, 0.11, 0.07, 0.10, 0.23, 0.18, 0.42, 0.13, 0.25, 0.35, 0.32, 0.23, 0.20 and 0.21, respectively. Genetic correlation between milking speed and production traits were negative, ranging from -0.22 to -0.10. Genetic correlation between herd life and type score was 0.87 and herd life and milking speed was 0.61. Genetic correlations between production traits and herd life and production traits and somatic cell score were unfavorable. Genetic correlations between herd life and milking speed, herd life and type score, herd life and milk yield, and herd life and somatic cell scores were 0.61,0.14,0.42 and -0.23, respectively.Udder traits were highly correlated with production traits and scondary traits. Where the highly correlated traits were fore udder attachment, rear udder width, teat displacement and udder vein, the genetic correlations ranged from -0.36 to 1.00. indicating that the production traits and secondary traits will be improved by selecting udder traits. Environment has a great effect on secondary traits, the management and milking stage were the main factors to influence milking speed. herd life and somatic cell count.