Based on ERA-20C, ERA-Interim and ERA40, the ECMWF's reanalysis data, the interdecadal variation characteristics of the boundary-layer height of arid and semiarid areas over East Asia and North Africa spanning from 1900 to 2015 was analysed. The results showed that: (1) From 1900 to 2015, the average boundary layer of Arid and Semiarid Areas of East Asia and North Africa were 755 m and 834 m, respectively. It presented significant upward trend over East Asia with the climate tendency rate of 2.0 m·(10a)~(-1) and the decadal oscillation cycle of 20 years, and it presented downward trend over North Africa with the climate tendency rate of -0.6 m·(10a)~(-1) and the decadal oscillation cycle of 40 years. The year 1964 and 1940 were the significant turning point of East Asia and North Africa, respectively. After 1964, the boundary layer height of East Asia had a apparent rise and the boundary layer height's oscillation amplitude of North Africa increased obviously after 1940. (2) In arid and semiarid areas over East Asia, the most obvious upward trend region was at the east with the climate tendency rate of 10.7~12.4 m·(10a)~(-1), followed by central section, with the climate tendency rate of 3.8 m·(10a)~(-1), and the slowly upward trend region was at the north, with the climate tendency rate of 0.4~1.8 m·(10a)~(-1), the Taklamakan Desert showed downward trend with the climate tendency rate of -1.2 m·(10a)~(-1). Meanwhile, in the decadal fluctuations, the severe concussion presented in the sixties and seventies of East Asia boundary layer height was mainly associated with the change of central and east regions. (3) In arid and semiarid areas over North Africa, the central and north regions showed significant downward trend with the climate tendency rate of -5.1~-1.48 m·(10a)~(-1), and the south region showed upward trend with the climate tendency rate of 0.8~2.5 m·(10a)~(-1). However, in the decadal fluctuations, the intensified concussion after the forties of North Africa boundary layer height was mainly associated with the change of south region.