Abstract: The Fen River rises in Guancen mountain within the boundaries of Ninwu county in the northwest of Shanxi province. It is the largest river in Shanxi province. It is 695 km long. The flood plain grassland covers about 770km². The floodplain of Fen River is rich in diversity of vascular plant, including 74 families, 284 genera, 614 species based on survey. Among them there are 605 species of seed plant, which belong 279 genera and 69 families. In composition of the floristic geographical elements of the genera and the species, the temperate elements take dominant position. On the composition of specific geographical element, endemic to China is most marked difference to the genera. This is reflected the temperate character of the flora as well as a zonal characteristic of the composition of the flora. The composition of Raunkiaer's life-from are arranged cryptophytes(51.07%) > therophytes(33.06%) > hemicryptophytes(9.42%) > phanerophytes(4.79%) > chamaephytes(1.65%).In composition of Drude's life-from, Perennial herb and annual herb take dominant position(92.56%).In composition of ecological types, there are Mesophytes (70.52%), Hydrophytes and hygrophyte(21.66%), Xerophytes(7.82%). Vascular plan in flood plain of the Fen River are divided into 11 groups according to their economic purposes. The result is objectively reflected status of seed plant diversity in flood plain of the Fen River. Furthermore, four strategies for conserving biodiversity in flood plain of the Fen River were suggested.

Key words: flood plain of Fen River, grassland, seed plant, diversity, conservation strategy