There are many interesting physics phenomena in producing diffusing arc plasma by magnetically driven rotating arc. The large-scale arc hollow electrode plasma generator with an outer magnetic filed is designed and a photogrammetry is built to investigate the arc structure and arc movements in the argon under the atmospheric pressure with the aid of a high-speed digital camera. Typical arc structure

under arc currents and external magnetic field

is a developing and increasing spiral one

which breaks and new arc column is re-constructed as plasma jets towards the anode appearing nearby the cathode. The rotating frequency of anode spot of the arc is analyzed with statistics mean. The arc voltage fluctuation frequency resulting from arc movement is obtained by using the Fast Fourier Transform (FFT) method. The analysis results show that large voltage drop is attributed to the breaking and reconstruction of multiple layer spiral structure of the arc

and small voltage fluctuations are probably caused by arc lengthening and shortening during the arc root jumping on the anode.