The objective of this article was to study the effects of dietary supplementation with chromium-picolinate on production performance, blood biochemical indexes and hormone levels of dairy cows and their mechanism under heat stress. Twenty-four dairy cows (15-24 days after parturition) were randomly divided into four groups which were randomly allocated to one of the four treatment diets (A, B, C and D). Diet A was basal diet, and diets B, C and D were added with chromium at the level of 3.6, 7.2 and 10.8 mg chromium/(head·day) based on diet A, respectively. The feeding trial lasted for nine weeks. Averaged THI was above 79 units during day period, which indicated that dairy cows were under serious heat stress. Results showed that chromium supplementation could improve the production performance of dairy cows under heat stress. The dry matter intake of dairy cows was significantly increased by adding chromium-picolinate (P<0.05). The milk yields, concentrations of blood glucose and IGF-Ⅰ, and the activities of insulin were increased significantly by adding 7.2 and 10.8 mg chromium/(head·day) (P<0.05). The concentrations of luteinizing hormone （LH） at the first day after oestrus, progesterone （P4） and LH at the tenth day after oestrus were significantly increased by adding 7.2 and 10.8 mg chromium/(head·day) (P<0.05). Compared with control group (group A), the days from parturition to oestrus of groups B, C and D were shortened by 1.85, 4.00 and 3.84 days, respectively (P<0.05), and conception rate in the period from parturition to oestrus was both improved by adding 7.2 and 10.8 mg chromium/(head·day). In conclusion, adding 7.2 and 10.8 mg chromium/(head·day) could significantly increase production performance of early-lactation cows under heat stress, improve the metabolism and regulate the reproduction hormone levels.［Chinese Journal of Animal Nutrition, 2010，22（2）:380-385］