A scheme of an oxygen input by particles at Arc Spraying is offered. Both external and internal diffusion processes are taken into account. The oxygen input was separately examined at arc-burning zone and spraying distance. At first the oxygen is dissolved in liquid metal drop up to a limit of saturation. Then slag formation begins accompanied by metal – slag interaction. Modeling of these processes was performed on a base of oxygen input/output mass balance. It was completed by computation of oxygen diffusion flows into gas and metal through interface surface. Mutual influence of alloying elements was also taken into account at slag formation on particle surface. The modeling results are represented in case of arc sprayed steel (1.1 C, 1.9 Mn, 0.8 Si). Propane - air mixture was used as a transporting gas. Good similarity with experiment data was achieved. As shown by calculations, basic share of oxygen input occurs in the arc-burning zone. The investigation results were used in core wire developing and gun designing as well.