In high-frequency electric resistance welding (HF-ERW), the hot rolled steel strip is cold-formed into a pipe shape, and the strip edges are heated by a high-frequency alternating current (AC) and subsequently compressed to form a joint without a filler material. The as-welded joint shows a characteristic hourglass or waist drum shape. In the past, the Gleeble thermo-mechanical simulator was used to understand the mechanism(s) of the joining process and the microstructure evolution during the HF-ERW. However, the low-frequency volume heating on the Gleeble thermo-mechanical simulator cannot simulate the characteristic HF-ERW thermal history of the industrially produced joints. To faithfully reproduce HF-ERW joints on a laboratory scale, a novel physical simulation system, which consists of a high-frequency induction heating unit, an MTS servo-hydraulic load frame, and a closed-loop temperature controller, is designed and developed. This novel physical simulation system, combined with the microstructure characterization using optical microscopy and scanning electron microscop, and thermodynamic modeling (using Thermo-Calc and DICTRA), is used to investigate the bond formation mechanism(s) for the HF-ERW of the X65 pipeline steel. A mechanism for the bond formation during the high-frequency electric resistance welding is proposed based on force, temperature, strain, and strain rate measurements.