High-speed welding technology are widely used in shipbuilding,petrochemical,power, metallurgy,automobile and other fields.Welding hot crack under transient thermal impact and mechanical constraint are easy to be appeared in welding process.The existing detections for hot crack mainly rely on the offline means after welding,which is absence of the online,accurate critical information for inhibition of the hot weld crack.The characteristics and difficulty of the online acoustic emission detection method applied to the hot weld crack were discussed.The inland and overseas research advances were reviewed from the acoustic emission dynamics model of welding hot crack,the modern signal analysis methods for acoustic emission signal of welding hot crack and advanced pattern recognition method.The existing key problems in the current research for the welding hot crack detection were pointed out and the approaches to these problems were discussed.