Abstract: The model of supply and demand of water resources was established, combined with meteorological, hydrological, soil condition, planting industry structure, vegetation and economic development of irrigation region in the middle reaches of Heihe river, northwest China to develop a calculation and evaluation model of regional supply and demand of water resources. After unified management of water resources in Heihe river basin between Gansu Province and Inner Mongolia in China, the amount of surface water from Heihe river decreased and that of groundwater increased, the volume of groundwater mining is increasing and the groundwater table is rising in studied regions now. The groundwater exploitation potential of irrigation region is less than the permissible utilization volume of groundwater, groundwater overdraft is remarkable in irrigation region. This paper has also proposed the measures to meet water security in the middle stream and related suggestion has been raised to guarantee this balance. It is found that water supply and water demand was safe in 1997, but water supply was not safe in 2003. If the water resources management, surface water and groundwater planning, the patterns and techniques of optimum utilization of water and land in this region would be tackled, the problem of the security of supply and demand of water resource and eco-environment is confronted with the baptism of Heihe river basin.

Key words: The middle reaches of Heihe river, Irrigation region, Water resources supply and demand balance, Evaluation on the security of water resources