To study the mechanism of interaction between ions and mid-infrared crystals and explore the preparation and properties of mid-infrared crystal optical waveguides, an optical ridge waveguide with a depth of 17.5 μm and a width of 14 μm was fabricated in MgF₂ crystals by ion irradiation combined with precision diamond blade dicing. The SRIM software was used to simulate the process of electronic and nuclear stopping powers of MgF₂ crystal irradiated by C⁵⁺ ions, and the mechanism of waveguide formation was analysed. The refractive index variation of the waveguide was simulated, and the near-field mode of the waveguide was experimentally measured and theoretically simulated. The propagation loss of the waveguide was reduced to 0.4 dB/cm by thermal annealing. The micro-Raman spectra show that there was no significant lattice damage in the waveguide region of the MgF₂ crystal during ion irradiation. The results show that ion irradiation combined with diamond dicing is a very mature method to prepare ridge waveguides, and the prepared MgF₂ crystal ridge waveguides have a wide application prospects in the field of mid-infrared integrated optics and optical communication.