In order to make the fire extinguishing system collect the correct partial voltage value of the sensor and accurately detect the fire, the residual voltage of the RC type linear temperature sensor is analyzed. Based on the factors such as the amplitude, frequency, and heating temperature of the excitation signal, the cause of the residual voltage of the sensor is analyzed. The results show that the residual voltage value is related to the amplitude of the applied excitation signal and the heating temperature of the sensor; the larger the amplitude of the excitation signal and the higher the heating temperature result in the higher residual voltage value.