Abstract: The effect of internal magnetic field and external magnetic field on twin-wire indirect arc shape was studied in this paper.The variation of internal magnetic field was obtained by changing the angle of wires.The external magnetic field was applied by excitation coil.The magnetic induction intensity was measured by Tesla meter,and the indirect arc shapes were captured by high-speed camera system.The experimental results showed that the magnetic intensity difference between the internal and external region of arc increased by decreasing of the included angle and increasing of applied transverse external magnetic intensity.As a result,which increased the extrapolation effect of electromagnetic force and the arc became long and concentrated.Applied longitudinal external magnetic field would deflect the indirect arc in the vertical plane of the twin wires,and the deflection degree increased with increasing of applied longitudinal external magnetic intensity.