Resonant pressure sensor, whose thermal gradient field is changed by variations in electro-thermal excitation, then influences the resonant frequency of the sensor, so different thermal excitation will produce different thermal stress, and then influences the characteristic of the sensor. For the thermal excitation resonant pressure sensor at different voltages excitant will produce different thermal gradient field, then influences the frequency of the sensor. Taking the advantage of lock-in amplifier, which can detect weak signal, an open-loop test experiment about the resonance output signal is carried out by using the method of alternating current excitation and pick-up with two-octave component. The results show the relational about thermal excitant virtual value and resonant frequency of this silicon microstructure resonant pressure sensor. Analysis about the result of the experiment is given, which can provide certain theories basis for the optimum design of the related parameter of this sensor, and have an important advice for the peripheral circuit design.