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The coupling relationship between land surface processes and atmospheric boundary layer is one of the key links and difficulties in understanding the thermal effect over the Qinghai-Xizang Plateau.Based on the surface and radiosonde observation data of Nagqu Plateau Climate and Environment Observation and Research Station in May， July and October 2019， this paper analyzes the surface energy budget， the daily and seasonal variations of vertical profile of atmospheric temperature and humidity， in Nagqu Area of the Qinghai-Xizang Plateau， and discusses the evolution law of the atmospheric boundary layer height in different seasons in this region.The results show that the convective boundary layer is 2842 m high in sunny days due to the influence of diurnal net radiation intensity during the observation period in May.It is 1481 m high in cloudy day， which is relatively low， and the strong convective weather may change it into a stable boundary layer.In the meanwhile， the exchange between the sensible heat and the latent heat in the near surface atmosphere provides energy support for the maintenance and development of the atmospheric boundary layer.The vertical profile of potential temperature and specific humidity can correctly reflect the seasonal difference of atmospheric boundary layer height in gqu Area.The height of the convective boundary layer is highest in May， less high in October and the lowest in July while the stable boundary layer is highest in July， less high in May and lowest in October.

Evapotranspiration (ET) is an important component of the surface energy balance and water cycle, especially in arid and semiarid regions. The characteristics of the actual evapotranspiration (ETa), which was calculated using the eddy covariance method, and the reference evapotranspiration (ET0), which was estimated using the Food and Agriculture Organisation (FAO) Penman–Monteith method, were analysed. This work focussed on the seasonal variations in evapotranspiration and crop coefficient (Kc) above the heterogeneous canopy of an arid oasis ecosystem in a cornfield of the Zhangye oasis in northwestern China. The results showed that in 2008, the total net radiation (Rn) was 2457.73 MJ∙m−2 and that the rainfall was 117 mm. The average wind velocity, air temperature, and specific humidity, which were observed 2 m above the ground surface, were 1.23 m∙s−1, 7.07 °C, and 3.66 g∙kg−1, respectively. The total ETa and ET0 were 654.69 mm and 1039.92 mm, respectively; thus, the ET0 was higher than the ETa. The difference between the ET0 and ETa was high in summer and autumn, and low in winter and spring. The ETa was greatly influenced by irrigation events, whereas the ET0 was not influenced by irrigation. The ETa and ET0 were both greatly influenced by meteorological elements. The Kc values were less than 0.5 outside of the maize-growing stage and greater than 0.5 during the entire maize-growing stage (from 20 April to 22 September 2008). The Kc values were 0.63, 0.75, 0.78, 0.76, 0.61 and 0.71 at the seedling, shooting, heading, filling, and maturity stages and the entire growth stage, respectively.