This paper provides a mathematical model, describing the simultaneous influence of two parameters which are the ignition voltage (Uz) and discharge currents (Ie) on the surface quality of SUS 304 stainless steel when it is processed by wire cutting machines. To get this result, the authors have conducted the processing of stainless steel using GS2532B wire cutting machines with the input parameters Uz and Ie set one by one at min and max values. After processing, the products were measured for surface roughness (Re). With the measured data, orthogonal experimental planning and construct equation were used to show the dependence of Ra on Uz and Ie. In addition, the authors used the Matlab software to create 3D graphs to describe the relationship between Ra and Uz, Ie. According to the equations and graphs published in this paper, engineers and technicians can establish a set of appropriate parameters of Uz and Ie to give products a specific roughness after being processed.