Abstract: In order to illustrate effects of water and planting density on root character of different ploidy wheat , three different ploidy wheat (the diploid Triticum monococcum, the tetraploid Triticum dicoccum, and the hexaploid Triticum aestivum ‘Changwu 134’) were planted in field experiment conducted in Yangling. Three planting densities (low, medium and high density, exactly 1, 2.5 and 4 million plants per hectare) were set, and two kinds of water conditions were taken as well respectively one with normal rainfall and irrigation while the other with none, to investigate the response of root dry weight, root length, water consuming characters to the density and water conditions. The results indicated that: the root dry weight at flowering stage did not decrease with the ploidy increase, root length of the tetraploid and the hexaploid was higher than that of the diploid under water-supply condition, the hexaploid was more sensitive to water while the water consuming showed no significant difference among the three ploidy wheat; the root distribution and proportion of total root weight and length in surface soil declined under water deficit, but the root distributed in the depth increased, so that the water in deep soil was used more efficiently; higher density brought in more competiveness in surface soil ,thus the root grew down and the proportion in depth increased, more water in deep soil was then taken. All above-mentioned results provide the theory basis for wheat breeding and planting in the arid and semi-arid area.