The mean annual and season spatial distributions of dust storm, fly sand, floating dust are given by using observations from 1970 to 2000. The reasons of causing the dust weather are analyzed. It is found that there was a dust strip passing from Wuwei via Jingtai and Baiyin and Huining to Tianshui and Huixian, the floating dust weather occurred frequently over there. The dust strip was consistent with the rainless strip from middle to south of Gansu Province, and with the lay of the land of northeast of Qinghai-Xizang Plateau. The dust strip is one of the reasons of desert area extending in middle and south of Gansu.