Abstract: The Baotou-Lanzhou railway crossed 45 km of Shapotou section of the Tengger desert,where there was 186 mm precipitation a year and sand dunes with more than 20 m relative height go at 4 m per year forwards to the southeast.Combing engineering and biological measures,the engineering system of wind prevention and sand stabilization began to be built without any irrigation after 1956.For half a century the system has insured the Baotou-Lanzhou railway straightway.Succession of plant-soil system for decades has endangered the stability of the protection system.In the evolvement from artificial system to natural one,vegetation underwent self-thin process from increase of coverage to decrease and from artificial shrubs to semi-shrubs then to herbs.Aeolian soil developed to Calcic-Aridisols with bio-crust.Redistribution of precipitation has changed thoroughly in the eco-system.The new pattern of water balance obviously affected the stability of the protection system.

Key words: plant-soil system, water balance, drought layer, bio-crust, arid zone