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Drainage ditches play an important role in maintenance of plant species diversity. We investigated plant species composition and diversity, and soil and water chemical properties in drainage ditches in the Hetao Irrigation Region of northern China. We compared species composition similarity within the same and among different drainage areas, and compared diversity of plant species, among different ditch sizes and slope positions. We identified a total of 70 plant species, which belonged to 64 genera and 30 families in the drainage ditch. The most frequent family was Compositae representing 15.7% of the total flora;Phragmites australis(Cav.) Trin. ex Steud was the most widespread species with a frequency of more than 60% in all plots. The highest similarity values occurred in lateral ditches within the same drainage areas, and in main ditches among different drainage areas. The coefficient of variation of total salt in soil was closely related to species similarity in all ditches. Ditch size and position were significantly correlated with the indexes of species diversity. Higher plant α-diversity occurred in smaller ditches and tended to be the highest at the transition zone and on the slope of the ditches. The response of species composition and diversity to environmental factors was significant for saline concentrations. Reducing the current water and soil saline contents, while maintaining current slope soil nitrogen content was suggested as an optimal way of maintaining high species diversity. [ABSTRACT FROM AUTHOR]