This paper analyses the thermal regime of the underlying surface in the cul-tivated area of Hulun-Bir steppe and discusses the increase of atmospheric dust content over the area caused by the variation of the thermal condition of underlying surface after cultivating.The result of observation shows that after cultivating the albedo of the cultivated land is about 0.13 to 0.18, with a mean value of 0.16. The albedo for grassland is about 0.16-0.21, with a mean value of 0.19. The surface temperature of cultivated land is about 3-4℃ higher tham that of grassland during daytime, so that the effec-tive radiation of cultivated land is larger than that of grassland. The heat balance for cultivated land is quite different from that of the grassland. The net radiation on the grassland is mainly used for the evaporation, which constitutes about 60% to 70% of radiation balance, and is larger than that of the cultivated lanid. But the turbulent heat flux on cultivated land is larger than that on grassland, about 4 times larger at noon, sometimes even 10 times larger. The turbulent) heat flux on cultivated land constitutes about 60% of radiation balance so that the net radiation of cultivated land is mainly used for the turbulent transport of heat into the air.The relationship between the diurnal variation of the turbidity of atmosphere and the turbulent heat flux in spring over Pa-Kshi Farm shows that the turbulent heat flux increase rapidly following the development of turbulent thermal instability. In the meantime, the increasing turbidity of atmosphere over cultivated area is due to the increasing transport of dust particle from the surface of the earth to the air. This is the cause why there occurs frequently the dust bowls on the cultivated land of Hulun-Bir steppe during April and May.