Based on a novel surface acoustic wave (SAW) one port resonator, a SAW Staphylococcus aureus (S. aureus) biosensor was designed and fabricated. This sensor adopted a resonator structure with a built in sensitive area in the middle of the interdigital transducer(IDT). Firstly, we analyzed the response mechanism of SAW biosensor according to the perturbation theory. Then, by combining the coupling of modes (COM) theory, the frequency response curve of the resonator was obtained. The measured results of the network analyzer showed that the frequency response curve of SAW resonator was consistent with the simulation result, and the resonator had the advantage of high quality factor. This structure was used for preliminary detection of Staphylococcus aureus in the experiment, and the linearity of the detection results was good, which laid a foundation for the next step of realizing the specific real time detection of S. aureus by SAW sensors.