Abstract: Heihe River Basin is the second largest inland river basin in the arid northwest China. In arid inland basin, the core problem is water resources, while the core area is an oasis. In modern oasis, the "water resource" of the actual use of the unit is "irrigated district". Oasis formed through the integration of complex irrigated areas. Under the strong control and guidance of the artificial canal system, water supply quantity determines irrigation district, and irrigated land determines population carrying capacity, water-soil-human systems exist a high degree of interdependence and symbiosis. One of the factors beyond the reasonable range, will be a profound impact on the system-wide coordination and stability as well as the direction of succession. Therefore, the law of formation and development of settlements from the coupling relationship between micro process, micro mechanism and the micro pattern, must be discussed to analyze the pattern of settlements which distributed in different types of irrigation district, to explore the coupling relationship between "Point"(settlements) "-corridor"(canal systems and road network)and "surface"(irrigated land). Applied nearest distance index, the paper analyzes spatial coupling relationship between the settlements and irrigated lands, as well as canal systems for 39 irrigation districts in Zhangye Oasis, Gansu Province, China. The results showed that:in the 39 irrigated districts,there are 22 irrigation districts in which NNI value is less than 0.5, settlements show aggregated distribution trend, but the space differences are significant. Hillside irrigation districts are often formed by independent river, its scale are smaller. They have limited water resources and poor level of assurance, water resource have stronger restrictive for human activities and settlements. Human activities are squeezed in a relatively limited space, which showed aggregated distribution of population and settlement. Irrigated districts located in abdomen of oasis, because of rich water resources and the development of a long history, detente human-land relationship,population and settlements showed discrete distribution trend. From the independence irrigated districts(Xinba Irrigated District)located in hillside to the irrigated district(Pinchuan Irrigated District)distributed in the oasis edge,and then to the irrigated district(Yinke Irrigated District)located in abdomen of oasis, the average near distance between settlements and irrigable land/canal system/road network are gradually increase, illustrate the relationship between irrigable land, and canal, as well as settlements come progressively closer. From the microscopic point of inspection, inside irrigation districts, settlements and water-land resources maintained very close relationship, the average nearby distance between settlements and irrigated land, settlements and canal systems, settlements and road network, are gradually increase. Settlements and the canal systems, as well as irrigated lands,exhibit significant feature of "hydrophilic type" and "pro-land type". "Point"(settlements) "-corridor"(canal systems and road network)-"surface"(land) exists a very close interdependence. Previous research on inland river basin in arid region, were often carried from the macro perspective of "mountain-oasis-desert", this paper, to break the routine, select micro scale(irrigated district)to study the coupling relationship between settlement and the water and land resources from micro mechanism, microscopic pattern, which allows people to see more clearly, water resource is how to influence the settlement distribution in oasis.

Key words: irrigated district, settlements, irrigated land, canal system, NNI, Zhangye Oasis