Abstract: Based on the mechanism of spatter, the contracting process of short circuiting bridge is analysed and a quantitative description is given. The rules of the contracting process are shown and the contracting degree is tested on real bine. On the analysing base, a specific power source, with the composite external characteristics of permanent voltage and sudden fall, is proposed unprecedently. It controls the bridge contracting process in real bine, and results in a stable short circuiting arc welding process with much low spatter.