In this paper,a magnetic acoustic surface wave(MSAW) resonator based on flexible polyimide (PI) substrate is studied and fabricated by solving the technique problem of preparing amorphous soft magnetic thin films on flexible substrates. By sputtering and depositing amorphous FeCoSiB magnetostrictive film and ScAlN piezoelectric film on flexible polyimide (PI) substrate, the interdigital electrode was fabricated by photolithography and the layered structure of IDT/ScAlN/FeCoSiB/PI was formed, the flexible MSAW resonator was fabricated successfully. The structure and surface morphology of the films were analyzed by X-ray diffraction(XRD) and atomic force microscopy (AFM). The static and high frequency magnetic properties of FeCoSiB films were measured by VSM and short-circuit microstrip method.Finally,the device is tested on the probe platform by vector network analyzer and compared with the simulation results of COMSOL.The experimental results showed that the MSAW device had two resonance peaks,of which the Rayleigh wave appears at 28.32 MHz and Lamb wave appears at 93.69 MHz.