When slurry-assisted soil-pressure balance shield construction is used to penetrate the existing line in the karst strong development area, the poor control of shield tunneling parameters will cause large disturbance to the existing line under the coupling effect of train load and cavern, resulting in excessive settlement or uplift bulge, which seriously threatens the safety of the existing structure. The influences of karst cave and train load on stratum deformation are analyzed by numerical simulation combined with field measurement, based on the project of building a comprehensive pipe gallery under a subway line in a city. Meanwhile, the effects of different slurry-assisted shield tunnelling parameters on the ground surface and the subsidence of the existing operating subway lines are studied under the coupling of the karst cave and train load. Combined with the ground surface monitoring results show that: Under the coupling effect of train load and karst cave, increasing the synchronous grouting pressure and the face grouting pressure appropriately can effectively control the deformation of the formation. The conclusion of the study can provide a reference for the future slurry-assisted shield structure under the existing line in karst area.