Abstract: In the marble of Tieling formation at Yangshigou, the sheath folds that are perpendicular to the maximum principal strain axis X and perpendicular to the intermediate strain axis Y are found and the deformation characteristics and mechanics are analyzed in the paper.The results show that sheath folds reflect the ductile shearing direction generally in SSE direction 150°~160°, and formed later than formation time of the marble of Tieling formation.