Abstract: Aiming at the problem that the use ofК190Лкwelding machines for welding PD3 60 kg/m rail makes the quality of joints not satisfy the TB/T1632 - 91 standard because of the existence of grey spots in welding joints, the relationship between the quality of rail joints and the eigenvalue of high frequency data at the acceleration stage of rail smelting is analyzed, and the process eigenvalue of rail flash welding is obtained. The research contributes to establishing of the on-line control system of welding quality.