Using the Langmuir probe method, the reactive plasma parameters were studied in different ratios of oxygen and nitrogen concentrations in a DC cylindrical discharge device. The plasma parameters such as plasma potential, electron density and electron temperature were extracted from the current-voltage characteristic’s curve of Langmuir probe to find the optimum conditions for deposit the oxynitride thin films. Chromium thin films were exposed to various O2/N2 partial pressures to obtain optimum value for produce of oxynitride chrome thin films. In addition, the influence of the magnetic field on the structural properties of the chrome oxynitride thin films was obtained. It is observed that for equal percentage of reactive gases, the optimum condition of the plasma discharge takes place in which the crystalline phases of oxynitride chrome thin films appear.