Abstract: To investigate the disturbance patterns caused by the railway tunnel excavated by the boom-type road? header, which crosses undere the existing surface structures in karst strata, a karst cavity unit extraction algorithm was proposed, the three-dimensional refined finite element model was established based on a roadheader-excavated railway tunnel project, the ground settlement, the settlement and tilt rate of the existing surface structure were analyzed, and the impact of karst filling quantity on surface settlement trough was explored. The results indicate that:(1) Due to the foundation stiffness of the existing surface structure, the settlement trough caused by the boom-type roadheader construction exhibits segmented characteristics: it is approximately linear under the building and conforms to Peck formula form outside the building; (2) During the under-crossing process, the settlement and tilt rate of the existing surface structure show a three-staged variation trend, corresponding to the three-stage construction of boom-type roadheader; (3) The impact of karst cavity filling quantity on surface settlement exhibits a staged trend: When the filling quantity is less than 70 %, the maximum surface settlement decreases with increasing filling quantity. When the filling quantity exceeds 70 %, the maximum surface settlement remains stable.