Focused on trace gas detection technology based on cavity ring down spectroscopy in the DFB laser wavelength stability requirements,taking EPM1654 laser module for example, the unbalanced bridge circuit for temperature measurement based on NTC thermistors is deeply analyzed. The guantitative analysis and weights comparison of the temperature measurement error caused by a variety of factors, which include the nominal value of the error and drift of passive resistance of the device,the active operational amplifier offset voltage and drift,noise and quantization error of the AD converter,thermistor resistancetemperature nonlinear fitting,shows that the nominal value of the reference resistor error and drift is the primary factor affecting temperature measurement accuracy. By the comprision of temperature measurement accuracy of differernt bridge reference resistior,we find that within the ambient temperature, the NTC thermistor which has the similar resistance to the reference resistarce helps to reduce measurement error.