Abstract: It is necessary to test surface defect for the aluminum alloy fusion welding of launch vehicle tank by the liquid penetrant method each time after the welding has been repaired. The characteristics of aluminum alloy fusion welding，the influence of different welding zone on electric conductivity and influence of different shape on eddy current testing signal are analyzed and studied. The result shows that the 3.0 mm×0.2 mm×0.3 mm artificial defect of welding surface can be tested by array eddy current testing method.