采用剪切错台模型，研究新建盾构隧道正交下穿对上方既有地铁盾构隧道的影响.考虑新建隧道下穿时刀盘附加推力、盾壳摩擦力以及注浆附加压力在既有隧道轴线处产生的附加应力，将既有地铁盾构隧道简化为由剪切弹簧连接的弹性地基短梁，运用最小势能原理并采用合理的位移试函数，建立计算方程来求解既有隧道的竖向位移值、盾构环之间的错台量、环间剪切力值以及这三者随着新建隧道掘进的三维变化过程.研究结果表明：用剪切错台模型和最小势能原理计算得到的既有盾构隧道竖向位移值与实测值较为吻合；既有盾构隧道竖向位移最大值处的隧道错台量接近0，在竖向位移曲线的反弯点处隧道错台量和环间剪切力值最大；随着新建隧道的掘进，既有隧道的竖向位移、错台量和环间剪力值不断增大，最后趋于稳定.Model of shield tunnel considering the shearing dislocation was used to investigate the effect of the new shield tunnel undercrossing on existing tunnels. In light of the fact that the additional stress along the central axis of the existing tunnel was caused by the bulkhead additive thrust, the friction force between shield and soil, and grouting pressure in the process of undercrossing shield tunnel construction, the lining ring of shield tunnel was regarded as a series of short elastic foundation beams connected by shear spring. An equation was developed by the principle of minimum potential energy, and three-dimensional change process of the vertical deformation, shear force and dislocation between rings with the excavation of the new tunnel were worked out. The research shows that the vertical displacement value calculated by the proposed method combined with the shearing dislocation model and the principle of the minimum potential energy agreed well with field test data. The dislocation of the segments where the vertical displacement is the maximum is close to 0. The maximum value of segment ring's dislocation and shearing force appears at the inflection point of vertical displacement curve. With the excavation of the new tunnel, the vertical deformation, shear force and dislocation between rings of existing tunnel increased and finally stabilized.