A new method of fusion pulse + short circuit mixed welding（MUP） was developed based on the panasonic digital welding machine GP5 in tangshan. MUP adopts precise pulse+short circuit waveform control technology,which can effectively reduce welding heat input,completely avoid the occurrence of arc extinguishing and upper combustion,indicating that the process of MUP welding is stable. The influence of welding speed,welding frequency and welding current on the shape of fish scales was studied by the single variable method,and the empirical formula of distance between adjacent fish scales was derived. The test results showed that,the spacing between adjacent scales was mainly determined by the frequency of welding and welding speed. With the increasing of welding current,the spacing between adjacent scales in basic remain unchanged when the frequency and the welding speed was fixed.When the welding speed increased or the welding frequency decreased,the distance between adjacent fish scales increased.