Abstract: The experiments have been caried out by flash butt welding of the ferrite spheroidal graphite cast irons with solid stick of 20 steel. By changing beta voltage 4~8 standing, voltaic time 3~5 seconds, the microstructure and tension strength of welded joints were measured. The results show that the welded joints consist of three zone. When the voltaic time remains unchanged, the tension strength of welded joints would become lower and then become higher. When the beta voltage remains unchanged, the tension strength becomes higher with the imcreasing of voltaic, time. When the beta voltage is 8 standing and the voltaic time is 5 seconds, the tension strength of the welded joints is up to the maximum 370.8 MPa, which is 90.4% of 20 pipeline steel and 83.7% of spheroidal graphite cast iron.