Abstract: Detailed observation line method has been used to investigate the joints of Zizou iron mine which was recommended by International Society for Rock Mechanics. Discontinuities spacing and dip angle have been counted with column diagrams. There are joint fissures and disintegrate structure rock mass in the roadways. Contour plot and major planes table have been drawed to analyze the joints survey data of Zizou iron mine by geological software Li zheng. At the same time the method of mathematical statistics has been used to analyze the geometric characteristics of each set of joints. The criterion of tunnel stability has been introduced into the roadways. Jonints are harmful for stability of rock mass of Zizou. We suggested that the anchor reinforcement or concrete spraying should be used.