The flora of Yihuang Mergus squamatus provincial nature reserve were surveyed and analyzed. The results showed that: (1) 776 species of spermatophytes affiliated to 428 genera in 119 families were discovered in the nature reserve, the families of flora were dominated by Gramineae (47 genera/80 species, similarly hereinafter), Compositae (35/51), Rosaceae (13/37) etc., the genera of flora were dominated by Polygonum and Rubus. (2) There was a high proportion in genera and families which contain one to four species, indicated the differentiation of the flora in this nature reserve. (3) The distribution types of families could be classified into 8 distribution types and 7 subtypes, and the ratio of tropical geographical elements to temperate geographical elements of families were 2.43, showed a tightness relation with tropical flora of the families in this nature reserve. Furthermore, the high proportion of cosmopolitan elements in families implied the intrazonal feature of the flora. (4) The distribution types of genera could be classified into 14 distribution types and 15 subtypes, and the ratio between tropical geographical elements and temperate geographical elements of genera were 1.05, suggested that the flora transitional character from tropical flora to temperate flora. The floristic characteristics show that the nature reserve provides an advantageous habitat for Mergus squamatus to winter, which is an extremely endangered bird affirmed by BirdLife International.