Abstract: The northwest peony cultivars are very unique among numerous cultivar groups in China. All the cutivars have blotches on the base of petals. According to the field survey and then referring to documents, we find the blotches varies very much in position, size, color and morphology. There are two positions of the blotches: close to the base and depart from the base. The colors of the blotches are mainly brown-red, purple, brown, black-purple. The size of the blotches, according to the proportion of their heights relative to that of petals`, can be divided into four types: very large, large, medium and small. And the morphology of the blotches have 10 types such as ovate, oblong and circle etc. The blotches can be described in order of color, size and morphology. Besides, the blotch bleed-through or not and the white lines on the center of the petaloid stamens are all in rich variation. All of the above greatly promote the flower ornamental characteristics of the Northwest tree peony cultivars.