BaxSr1-xTiO3 (BST) and its composite films have been studied for the improvement of the tunable performances via nano-structual control. The strong correlation between strain and tunability similar to that between strain and permittivity was confirmed in the epitaxial BST x=0 films, indicating that the high tunability of BST is strongly related to its high permittivity. The "oriented" nano-composite films composed of BST x=1 and CeO2 i.e. low-K dielectric, have achieved rather high tunability as compared to the significantly lowered permittivity. The obtained composite films also benefit from a suppressed temperature dependence of permittivity and tunability.