Abstract: In order to explore the expression of heat stress protein 70 ( HSP 70), the relationship between HSP 70 and temperature humidity index (THI) and the different breeds expression of HSP 70 in heat stress in blood lymphocytes. We used immunology and molecular biology methods to study the influence of environmental factors THI on Holstein and Jersey×Holstein F1 dairy cows. The result show that: (1) during heat and no stress period, the Holstein dairy cows can express HSP 70. Comparing serious heat stress period (THI 93.5±2.1) with moderate heat stress period (THI 76.7±2.6) and no heat stress period(THI 56.5±1.7), the expression of HSP 70 was 1.9 times (P<0.01) than that of moderate heat stress period and 6.9 times (P<0.01) than that of no heat stress period. The expression of HSP 70 in moderate heat stress period was 3.6 times (P<0.05) than that of no heat stress period, the relationship between the expression of HSP 70 and THI were positive(P<0.01)(R=0.91), THI rise 1 unit, the expression of HSP 70 increase 2172 OD/mm2. (2) The expression of HSP 70 in Jersey×Holstein F1 dairy cows were higher than that of Holstein dairy cows (P<0.01) during serious heat stress period (THI 95.3).