Abstract:The developmental process of root in Polygala tenuifolia Willd. was studied by anatomical methods, and the structures of the one-year-old and two-year-old main roots were compared. Meanwhile, the main medical composition and storage nutrition of the root was localizated by histochemistry. Polygala tenuifolia is taproot system, which is medicinal portion. The development of the root underwent four stages: promeristem, primary meristem, primary structure and secondary growth. The apical promeristem was originated from radicle and consisted of three initial groups, and they prossessed the typical cytological characteristics of meristem. The primary meristem consisted of calyptrogen, primordial epidermis, periblem and plerome, while the primary structure consisted of epidermid, cortex and central cylinder. Primary xylem is diarch. The secondary growth mainly depended the activity of the vascular cambium and cork cambium. Secondary xylem composed of large vessels, wood fibres and little xylem rays. A lot of phloem parenchyma cells, a small amount of sieve tubes and companion cells built up secondary phloem. The vascular has one or three flats cells. The cork cambium originated from the pericyclic cells and created multi layer of phelloderm parenchyma cells. The infrastructures were identical 0between one-year-old main root and two-year-old main root, but phelloderm cells are more than ten layers in two-year-old main root. The reserve substance was mainly oils and little polysaccharides in Polygala tenuifolia root. The tenuifolic saponins existed in all parenchyma cells. Xanthones accumulated in the cork cambium, phelloderm parenchyma cells and secondary phloem.