Abstract: Field observations of air temperature, relative humidity and atmospheric pressure in high-altitude regions were carried out at the sites near the transmission line corridors in Tibet with an altitude height higher than 4300 m, and the field observation data of three different altitudes with over one year duration were obtained. The impact differences of air temperature, relative humidity and atmospheric pressure on air density in high altitude regions were determined. The mean value, maximum value and minimum value of the observed air density at three typical high-altitude sites were statistically analyzed. Based on three types of statistical parameters, the decrease ratios of the observed air density relative to the standard air density were calculated respectively. The decrease ratios of air density at the three observation sites are basically higher than that proposed in applicable standards, which means that when the altitude heights are in the range of 4300 m to 4900 m, the anti-wind design of transmission lines is on the conservative side if the air density proposed in the applicable standards is adopted. When the observed maximum air density is proposed for design, the basic wind pressure for the regions with the altitude higher than 4300 m will be decreased by at least 31.7% compared to the value determined by standard air density. The results can provide a reference for anti-wind design and maintenance works of transmission lines in high-altitude regions.