Abstract: 【Objective】Transplanting Astragalus membranaceus var. mongholicus seedlings with different root thickness by flat planting,and harvesting the biennial and triennial plants,to explore the effect of seedling root thickness on the growth,development,yield and quality of root in different harvest years.【Methods】The tested seedlings were divided into three experimental groups of low,medium and high according to the middle and upper part of the maximum root thickness,and they were planted in a trench with flat planting.The images of biennial and triennial root sections of Astragalus membranaceus var. mongholicus were collected,and the middle and upper part of the root thickness,total root length,root fresh weight,root dry weight,yield,and the contents of calycosin-7-glucoside and astragaloside were determined.【Results】 Although the roots of the biennial seedlings were smaller than those of the triennial ones,the root quality was better.Compared with the biennial seedlings,the middle and upper part of the root thickness,total root length,root fresh weight and root dry weight of the triennial ones were increased.Among them,the medium group had the largest increase in root fresh and dry weight of the triennial seedlings,which was elevated by 61.4% and 61.8% than those of the biennial ones.The yields of the triennial seedlings in the low,medium and high groups increased by 21.0%,59.7% and 44.3% respectively compared with the biennial ones.And the output of the medium group was the largest,reaching（13 546.77±419.95） kg/hm².In the high group,the content of calycosin-7-glucoside in the root of triennial Astragalus membranaceus var. mongholicus was the highest,which was 0.078 4%,and the content of astragaloside in the root of biennial Astragalus membranaceus var. mongholicus was the highest,which was 0.070 6%.【Conclusion】The flat planting of seedlings was more suitable for the high-quality production of the biennial Astragalus membranaceus var. mongholicus,especially for the biennial seedlings with the middle and upper part of the maximum root thickness between 8-10 mm.

Key words: Astragalus membranaceus var. mongholicus, Seedling root thickness, Yield, Calycosin-7-glucoside, Astragaloside