The Boundary Layer Height (BLH) of the arid and semiarid regions in East Asia and North Africa (19002010) is compared by using the reanalysis data of ERA-20C of the European center. The result reveals differences of spatial distribution and time variation of different climate zones' BLH in the two regions. It shows that there is a close relationship between the spatial distribution of the BLH and the degree of climate wetting and drying, and is also affected by the altitude and the distribution of rivers and lakes. The BLH in the arid and semiarid-semihumid transition zones is increasing in East Asia and North Africa. The BLH in the extreme arid region, the arid-semiarid transition region and the semiarid region is increasing in East Asia but decreasing in North Africa. Extreme arid regions contributed the least to the overall annual change of BLH in arid and semiarid regions, with 11.05% in East Asia and 3.68% in North Africa. In East Asia, semi-arid regions had the largest contribution of 23.74%, while in North Africa semiarid-semihumid transition zones have the largest contribution of 28.89%. The changes of BLH in both regions contain oscillations with periods of 60 a, 30 a, 10 a, 5~7 a and 2~4 a. In the long-term cyclical changes, the BLH of the two regions are basically in an anti-phase relationship, and in the short time scales, it is in the relationship between the anti-phase and the same phase alternates. In the long-term change of BLH, the BLH of each season in East Asia is increasing in 111 years, while the BLH in North Africa is increasing in winter and decreasing in the other three seasons. Among the interannual changes of BLH, summer dominates the interannual changes of BLH in the whole region, with East Asia contributing 58.50% to inter-annual changes and North Africa contributing 57.52% to inter-annual changes. And the annual change contribution rate of autumn in North Africa is more than twice that of East Asia.
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