Despite that the requirements on the welding technology specification,welder qualification and welding operation for slot welds are defined in D1.1,[Steel Structure Welding Specification] and D1.6,[Stainless Steel Structure Welding Specification] of AWS,there are still cases that the welding operations for slot welds are mixed up with those for groove welds and fillet welds,resulting in quality incidents attributable to defects in slot welds. In view of such problems as development of the procedure for repair of slot welds and the welding operation techniques required,the cases in construction of steel structures and modules at project sites are analyzed,based on the repair of conventional welds,and the technical methods for repair of slot weld are put forward in accordance with the AWS specification requirements,including removal of defects,groove preparation and laying down the welding procedure for repair. And the operation techniques for repair of slot welds in various welding positions are introduced in detail.