注浆成型螺纹桩采用后注浆技术形成桩侧螺纹，有利于在软土地区施工，目前已开始应用。基于螺纹桩上拔过程中螺牙附近土体的应力条件改变，采用摩尔应力圆分析螺牙附近破坏滑裂面的开展，得到了螺牙间距与螺牙突出尺寸的比值与滑裂面展开角之间的关系，给出了螺牙间土体从圆柱形滑裂面破坏向圆台形滑裂面破坏的判别条件。根据滑裂面的开展，将螺纹桩的抗拔承载力计算分为3种情况，采用极限平衡法得到了相应的螺纹桩抗拔承载力计算公式。最后，通过与有限元数值模拟以及实际工程算例对比，验证了文中方法的合理性。

The post grouting technology is used to format the screws of a grouting screw pile, which can be constructed easily in soft clay area and has been applied to engineering project currently. According to the stress change of soils around the screws in the uplift process of the grouting screw pile, the Mohr circle stress analysis is conducted to analyze the development of slip line along the screw; and it can also give the relationship between the angle of slip line and the ratio of screw pitch to screw dimensions，which is expressed in the mathematical equation of incremental normal stress and shear stress of soil around the screws. The condition to judge the shape change of slip line between the screws from cylinder to truncated cone is obtained. Based on the shape of slip line, the calculation of uplift capacity of screw pile can be divided into three cases, the formula of which is obtained through limit equilibrium method. The application and rationality of the presented method is proved by comparison with finite element analysis and a field test.