A loop thermosyphon system usually adjusts the airflow rate of the backplane according to the servers’ electrical powers to reduce the energy consumption of data centers and improve the Data Center’s security. However, the heat dissipation efficiency of server chips could be affected by reducing the airflow rate, which may cause chip damage. In order to analyze the effect of airflow rate variation on the thermal security of the chip, a physical model is established in ICEPAK based on the structure and operating parameters of typical racks, servers and chips. Based on the established physical model and a one-dimensional steady-state heat transfer model of a loop thermosyphon, a comprehensive model is established to simulation the whole cooling process of the loop thermosyphon system. By simulations of the comprehensive model, the effect of airflow rate on chip temperature under different server loads is studied. Under the standard working condition (27 ℃ indoor air temperature, 18 ℃ cold water inlet temperature, 1 400 m3/h airflow rate), when the servers’ load is 6 kW, the average chip temperature is 54.1 ℃, and the energy efficiency ratio of the loop thermosyphon is 60. To energy saving and server’s security of the rack, the airflow rate is reduced to 43% (600 m3/h) of the full airflow rate (1 400 m3/h). The average airflow velocity on the surface of the chip radiator decreases by 37%, and the thermal resistance between the chip and the air increases by 35%, leading to the chip temperature and the exhaust air temperature of the server increase to 75.7 ℃ and 56.5 ℃ respectively. Meanwhile, chips can still operate safely, and the energy efficiency ratio of the loop thermosyphon increases by 132%. When the servers’ loads decrease to 4 kW and 2 kW, the airflow rates reduce by 70% and 85%, respectively, and the energy efficiency ratios of the loop thermosyphon increase by 240% and 600%.