Based on the CERA-20C global atmospheric boundary layer height (BLH) reanalysis data from 1981 to 2010,this paper focused on the diurnal variation characteristics of the BLH data,including seasonal variation, chronological change and interannual variation of the Qinghai-Tibetan Plateau. The statistic showed that the BLH large value areas include areas above 5 000 m and some desert areas,Nyima is the source of the high-value area in boundary layer. BLH increases most dramatic from 03: 00 (UTC,the same as after) to 06: 00 and decreases from 09: 00 to 12: 00,the increase of the BLH can reach 948.67 m·(3h)-1 with a decrease of 760.02 m·(3h)-1,and reaching to the maximum value at 09: 00. This is a bit later than the non-plateau area whose maximum time is 06: 00. The average maximum value during thirty years can reach to 1982.764 m,and the maximum daily variation is up to 2901.21 m,both manifesting a high volume during the day and low volume at night. The maximum value of BLH is the largest in spring while the smallest in summer,but the minimum of BLH lies in summer and the smallest in autumn. The BLH of Plateau West Slope reaches a maximum in spring and autumn,but in hinterland it's in winter. The BLH of Plateau East Slope is quite low and steady. At 03: 00,the BLH changed monthly in a single peak characteristic. In addition to the steady change of inter-annual variability in spring,autumn and winter,the BHL of these three seasons all feature great fluctuation in the mid of 1980s,late 1990s and early 21st century. The BLH in winter has gradually increased in the past 30 years,especially in the early 21st century. In spring,the plateau hinterland of the Qinghai-Tibetan plateau above 5 000 m is in snow melting period,and the snow takes away the surface heat,making the surface temperature lower in spring. The BLH in spring is negatively correlated with the surface temperature,at the same time,the summer relative humidity is wavy distribution, and the minimum relative humidity gradient corresponds to the top of the boundary layer,and the height of boundary layer is higher in spring than in summer. When the boundary layer is highly developed,the elevation boundary and the subsidence movement are usually alternately in the plateau boundary layer,which provides some dynamic conditions for the development of the boundary layer.