Abstract: According to the bonding mechanism of continuous drive friction welding, a new method which can evaluate the quality of welded joint by using the rate of expeiling interfacial contamination has been proposed. And then, on the besis of the frictional weling features for tubular form and the above idea, the movement of metal particls within the plastic zone during equilibrirm torque stage in friction welding has been analysed. A model on the rate of interfacial contamination removement has been construced. Two groups of friction welding parameter were applied for 35 mild steel tubular specimen,and the width of plastic zone in the joint of spadmen has been measured by using metallgraphic exannnation; The predital asults and expexerimantal values of the plastic widths are good agreement.