When the ultrashallow buried underpass constructed with the method of pipe curtainbox culvert strides over the operation subway, the mound cleaning and excavation of foundation pit before construction often cause subway tunnel deformation. In order to ensure the safe operation of subway, the subsequent construction of pipe curtain and box culverts must be strictly controlled. In this paper, based on analytical calculation method, two mechanical models are established according to the difference between the equivalent gravity of box culvert and undisturbed soil. The force of pipe curtain is studied with elastic foundation beam model and ordinary beam model, and the two kinds of forces are derived respectively. The mechanical formula under the two calculation models is used to analyze the variation law of the force and deformation of the pipe curtain during jacking process of box culvert, which provides a basis for further study of the force of subway tunnel under pipe curtain.