The Mahu region is an important unconventional oil and gas accumulation block. During its development, it is observed that casing deformation damage occurred due to pressure escape, and conventional casing repair tools proved inadequate for meeting the repair requirements. Consequently, a casing-shaping tool was designed. To evaluate the effectiveness of the designed tool for repairs, an evaluation function for casing repair efficiency was established. A ϕ127 mm casing deformation model was created using the finite element method to simulate the process of casing deformation resulting from pressure escape in the Mahu region. Building upon this, a mechanical model of cone expansion-deformed casing was established to simulate the non-destructive repair process using the casing repair tool for the deformed casing. In the simulation, the inner area of the deformed casing was repaired from 8 354.54 mm² to 8 500.71 mm², representing an average increase of approximately 146.17 mm². The average casing rounding efficiency was found to be approximately 53.83%. The results demonstrate the significant reparative effect of the designed casing repair tool. This technology can serve as a valuable technical reference for ensuring the long-term wellbore integrity throughout its life cycle.