The electrode distance variance and capacitance style pressure sensor is talked about. The change rate of the pressure is treated as judging basis of whether the fault is existed. Make the bridge output signal as the sensor's output signal and one of the detection signal, also make the operational amplifier output signal as another detection signal. The expressions of each element in drift failure when in changeless input signal are obtained. and the change laws of them are analyzed. On the basis of these works it is verified that different elements' failure can be distinguished and solved. After such works the fault location and the fault evaluation are realized. The simulation tells that the value of the fault diagnosis's results are relatively close to the true value of the fault.