A layer of BaO Nd2O3 Sm2O3 TiO2(BNST) thin films were prepared by RF magnetron sputtering technique on LaAlO3 (100) substrates on which the bottom electrode has been fabricated, then the films were annealed to improve its crystallization. X ray diffraction (XRD) analysis showed that BNST film after annealing has good crystallization. We use plate capacitor structure to measure the frequency characteristics of capacitor. This paper mainly studies the BNST film capacitor's frequency characteristics. LCR and vector network analyzer tests shows that at the frequency of 1 MHz, the dielectric constant is 58.3, the dielectric loss is less than 2%, while at the frequency of 1 GHz ,the dielectric constant is 57.5, the dielectric loss is less than 3%. The results show that the frequency characteristic of prepared BNST film is stable, and basically meet the requirements for using in the microwave frequencies.