The utility model relates to a flash butt welding device of an R5-stage mooring cable. Two ends of a rod material are clamped by electrodes respectively, the electrodes are communicated with a transformer, clamping force is generated at the upper part, upset forging force is generated at the two ends, the extension length of the two ends of the rod material between the two electrodes is Lmm, the flash allowance is delta amm, the upset forging allowance is delta cmm, and the heating temperature of the rod material before welding of a chain ring is 850 DEG C-950 DEG C; the welding time is 80 seconds; and the quenching temperature is controlled to be 120 DEG C-160 DEG C and the tempering temperature is above 600 DEG C. The flash butt welding device of the R5-stage mooring cable can enable a crosspiece to be in tight contact with a chain ring body, prevent seawater from entering, further ensure that the chain ring has no deformation or gear disengagement or gear falling during long-term use and reduce the weight of the whole chain ring by 3%, and has the performances of high strength, strong toughness, corrosion resistance, low anti-fatigue property and anti-deformation property.