The voltage current property of the unbalanced magnetron sputtering (UMS) system has significant influence on the sputtering process and films deposition process. Based on the analysis of the relationship between unbalanced magnetic field and properties of the unbalanced magnetron sputtering system, according to Child law the model of the V-I property of the UMS system is set up. Comparisons between the model calculation results and the experimental data indicate that the model correctly expresses the relation between the unbalanced magnetic field and the discharge properties of the UMS system.