Electrically assisted friction stir welding is a promising way to improve liquidity of viscoplastic metal.However,this local heat source only can take into effect in a certain contact interface status.Semi-analytical model and FEM are adopted to analyze materials flow in electrically assisted FSW.Semi-analysis results show that Joule heating is validity with rotation speed 1 400 r/min and travel speed 400 mm/min.The maximum flow velocity is 0.033 m/s when travel speed is 400 mm/min,and it increases to 0.043 m/s with current assist-ant.Visco-plasticizing efficiency is a key factor to decide whether Joule heat is significant,and viscoplastic flow can periodically make cir-cuit short.Periodic torque,axial force and onion rings surface show dynamic flow process,which can be used to illustrate the dynamic con-tact resistance feature and correct the calculation equation of Joule heat.This paper is aim to point out the potential relation between visco-plastic flow,periodic torque and Joule heating validity.