In this paper, we have studied the tin oxide films deposition by DC magnetron reactive sputtering. We have investigated the discharge parameters such as discharge voltage and deposition rate and the discharge composition as a function of the input oxygen partial pressure. We have compared these results with the deposited films stoichiometry. In the constant current discharge mode, we observe, with increasing oxygen partial pressure, a decrease of the discharge voltage followed by a slight increase, and a drop of the deposition rate. For each experimental conditions, we measure the gas composition by mass spectrometry (glow discharge mass spectrometry mode and residual gas analysis mode (RGA)) and the deposited films stoichiometry by X-ray photoemission spectroscopy. The results are fitted by means of a model, taking into account the plasma-surface interactions. All the data are fitted by the same equation, with only four fitting parameters, namely the sticking-reaction coefficients of 0 and 0, on Sn and SnO surfaces. Our results show that the main reaction is the reaction between the atomic oxygen and the metallic part (Sn) of the substrate. This reaction is characterized by a sticking coefficient value (alpha(1)(0)) of 0.96.