Abstract: Metal transfer frequency are usually taken as the criteria to evaluate the process stability of short-circuiting arc welding. In this paper, the time dependency of the output impedance of the power source during the short-circuit period is analyzed at first, afterwards a current waveform for short-circuiting arc welding was proposed with the aim of eliminating instantaneous short circuit and improving the process regularity. Considering that the Ohm heat on electrode wire extension (EE) plays an important role in the wire fusion, a new method of EE real-time detection and EE variation feedfoward is developed. Finally, the paper presents a fixed-frequency short-circuiting metal transfer control system based on microprocessor MC68HC11A1, which incorporates EE variation feedfoward and transfer frequency feedback. Practice welding shows that the expected transfer frequency and the resultant process characteristics are achieved successfully.