A lowcost and highefficiency circuit was used to measure the wireless passive resonant SAW sensors in this work. DDS technology was used to generate RF signals with different frequencies to excite the SAW sensor. A power detector was used in the receiving circuits to measure the envelope curves of echo signals. By analyzing the envelope, the physical or chemical parameters can be measured via this circuit. The power of the excitation signal produced by this system is up to 10 dBm and the test time is about 0.5 s while the relative error is only 0.002 4% compared with the results from VNA. The results show that this circuit can detect the resonance frequency of SAW sensor reliability.