Abstract: Superconducting elliptical cavity is a thin-walled structure formed by stamping parts and electron beam welding, and there are inevitable deformations in the machining process, like cell tilt, cell off-axis and cell length deviation. Thus, the axial electric field flatness of the elliptical cavity is affected, and then the operating electric field gradient is reduced. Therefore, pre-tuning is necessary after the elliptical cavity finish processing. The pre-tuning of elliptical cavity is to improve the axial electric field flatness by reshaping the elliptical cavity, including the correction of cell tilt and off-axis, and the correction of cell length. This paper presents the simulation of possible deformation of elliptical cavity by COMSOL multiphysics software and analyzes the influence of cell deformation and tuning displacement on electric field flatness is analyzed, it can provide data reference for CSNS-II elliptical cavity pre-tuning and guide the designing and developing of pre-tuning machine. In addition, it determines the requirements of mechanical deformation to ensure the machining quality of elliptical cavity to meet the actual engineering requirements of CSNS-II.