Abstract: Clear G_bands were obtained in the mitotic chromosomes of metaphase and three prometaphases in which the chromosomes condensed differently (they were called prometaphase Ⅰ,Ⅱ,Ⅲ respectively) in Triticum tauschii (Aegilops squarrosa) by using the advanced ASG method.The G_banded karyotypes and G_band fluctuation were analyzed. The G_bands were closely adjacent, multiple and distribu ted all along the chromosome length in all the phases and stages. And these bands were thin,of similar size,and distributed evenly.The total number of G-bands reduced by 41%, 36% and 28% respectively, and the absolute length of chromosome complement shortened by 43%, 37% and 27% respectively, when cell mitosis proceeded from prometaphaseⅠ ,Ⅱ,Ⅲ to metaphase.It was quite obvious that G_band number reduction was almost equal in extent to chromosome lenght contraction. There were differences for each chromosome in the rate of reduction of G_bands and the absolute length. Their variation ranges were also different.The band number per μm chromosome length in metaphase,prometaphaseⅠ,Ⅱ,Ⅲ were 2.19,2.22,2.32 and 2.29 respectively. It was obvious that band number per μm chromosome length of different phases and stages had little difference.The nature of G_band in T.tauschii (A.squarrosa) etc. were discussed.