Abstract: SCR rectifier source is a new type of electric control arc welding power source.Its perfomance depends on the main and flip-flop circuits.The behaviour of the main circuit depends on the inductor and its parameter.The function of the flip-flop depends on the type of synchronous shift phase singnal and the mode of feedback control.In this paper,the relation between the feedback control mode and the source performance is analysed by using frequency domin analysis and computer simulation technique.The results show that a reasonable feedback control mode and its electric parameters are necessary conditions that make the SCR rectifier power source obtain optimum performance.