Thom-X is a 50MeV compact ring based on the Compton back-scattering which is being built in LAL, France. With a very short bend radius of 0.352 m, the nonlinear effects of the dipole fringe fields become critical to the beam dynamic . This paper compares the modelings of the dipole fringe field using four popular codes: MadX, Elegant, BETA, and Tracy3, and then discuss the proper model to have consistent results between the analytical calculation and the symplectic tracking of the Thom-X ring.