The beam form has a direct effect on the quality and efficiency of flexible forming using a combined plasma arc. But it is difficult to directly measure relative parameters of the combined plasma arc for its characteristics of high temperature and high energy density. In this paper, an image collection system was designed with a lens, a neutral filter, an interference filter and a CCD camera to overcome above problem. Furthermore, the acquired digital image of diagnostic face of combined plasma arc was implemented pre-processing such as removing noises, edge detection, histogram equalization, contrast enhancement, enhancing morphological features by using MATLAB. The results show that the digital image of combined plasma arc is successfully captured by means of the system, which will be helpful to further the diagnosis and analysis of parameters of combined plasma arc.