[Objective] The purpose of this study was to find out the prevalence of subclinical mastitis in dairy cows in Lankao county,and to provide reference for prevention and control of the disease in the future. [Method] Subclinical mastitis was detected in 547 lactating dairy cows from 3 large-scale dairy farms using the California Dairy Subclinical mastitis Test （CMT） method to investigate the relationship between the disease and parities,lactation stages and milk regions. [Result] The results showed that the positive rate of cows was 20.11% and that of milk area was 10.88%. The incidence rates of 1~2,3~4 and ≥5 parities were 13.37%,20.53% and 29.46%,respectively. The incidence rates of early,middle and late lactation were 15.11%,22.12% and 30.89%,respectively. The positive rate of milk area ranged from 8.59% to 13.16%. [Conclusion] The results showed that the incidence of subclinical mastitis was relatively low in Lankao large-scale dairy farms and there was a positive correlation with parity and lactation period,but no significant relationship with milk area.