Abstract: The sound and light alarm circuit of methane sensor based on traditional RBI needs a long response period, and it can't act with the automatic control. With the Surface Acoustic Wave (SAW) methane sensor being investigated, the better choice of high-performance processors STC89C52RC chip, using a direct frequency counting method, realizes the high-frequency signal automatic cycle detection among 50~450 kHz. With this design, the chip will drive voice chip to generate sound and light alarm action. The frequency measurement system for the SAW methane sensor has many features such as the simple microprocessor and easy implement of high precision frequency measurement. The application of active 12MHz time dependent frequency resonator can better improve the accuracy of the frequency measurement, which is mostly adapted for the application of SAW methane sensors.