SAW resonators are widely used in various wireless sensor applications. In order to achieve high update rate and high precision SAW measurement, a low-cost resonant SAW interrogation system is proposed in this paper. By using a low-cost six-port interferometer, the frequency of a passive SAW resonator can be measured accurately and quickly. By using delay line, the frequency measurement value can be simplified to the phase measurement value which can be evaluated in real time through the six-port network, that is, the frequency estimation can be obtained by comparing the introduced phase shift with the non-delayed signal. The results show that compared with the conventional design, the proposed design can provide a high update rate and lower system cost without complex signal processing. The experiment on 2.4 GHz frequency band has proved the feasibility and superiority of the proposed design, the accuracy is high and the measurement time is only about 3 μs.