Abstract: During the 1: 50000 regional surveys in the western part of the Wutai Mountains, the author conducted extensive structural measurements of the early Precambrian metamorphic series iu the area, collected a lot of data about structural elements, and ascertained through a geometric analysis the common development of both conical and cylindrical folds. According to the close genetic relation between the two kinds of folds, conical folds may he divided into three different genetic types, and the geometric features of their structural features on the stereographic projection diagram are correlated and discussed in details. Thus a better understanding of the nature and evolution of the fold structures in the area has been gained.