Based on the sputtering theory and molecular thermodynamics theory, a mediated composition model of SmCo-based multinary alloy films was established, and the effect of sputtering parameters on the film composition was discussed. Subsequently, the SmCo-based multinary alloy films were deposited on Si substrates by magnetron sputtering from Sm(Co0.62Fe0.25Cu0.1Zr0.03)7.5 alloy target. The composition of the films prepared by different sputtering parameters was measured. The results show that the dependence of the film composition on sputtering parameters observed from the model agrees well with the experiment results, which gives a favorable support to the acquired model