Development process of the black storm on May 5,1993 and the relation of development of squall line to the black storm are analysed.The results show that there exists a dry squall line in front of the cold front cloud system on May 5,1993,and the dry squall line develops further into explosive the black storm as it moves in desert area,in which the ground surface is strongly heated by solar radiation and the atmosphere is unstable stratification.Air flow ahead of the gust front rolls up dry sand on ground surface to generate sand wall of black storm.